U.S. patent application number 15/192562 was filed with the patent office on 2016-12-29 for colorless luminescent solar concentrators using colloidal semiconductor nanocrystals.
This patent application is currently assigned to Los Alamos National Security, LLC. The applicant listed for this patent is Los Alamos National Security, LLC. Invention is credited to Victor I. Klimov, Hunter McDaniel.
Application Number | 20160380140 15/192562 |
Document ID | / |
Family ID | 57601883 |
Filed Date | 2016-12-29 |
United States Patent
Application |
20160380140 |
Kind Code |
A1 |
McDaniel; Hunter ; et
al. |
December 29, 2016 |
COLORLESS LUMINESCENT SOLAR CONCENTRATORS USING COLLOIDAL
SEMICONDUCTOR NANOCRYSTALS
Abstract
Disclosed herein are embodiments of a composition comprising a
polymer or sol-gel and one or more nanocrystals. The composition is
useful as a luminescent solar concentrator. The nanocrystals are
dispersed in the polymer or sol-gel matrix so as to reduce or
substantially prevent nanocrystal-to-nanocrystal energy transfer
and a subsequent reduction in the emission efficiency of the
composition. In some embodiments, the polymer matrix comprises an
acrylate polymer. Also disclosed herein is a method for making the
composition. Devices comprising the composition are disclosed. In
some cases the polymer is the waveguide, in others the polymer is
applied as a coating on a waveguide. In some examples, the device
is a window.
Inventors: |
McDaniel; Hunter; (Los
Alamos, NM) ; Klimov; Victor I.; (Los Alamos,
NM) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Los Alamos National Security, LLC |
Los Alamos |
NM |
US |
|
|
Assignee: |
Los Alamos National Security,
LLC
Los Alamos
NM
|
Family ID: |
57601883 |
Appl. No.: |
15/192562 |
Filed: |
June 24, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62185414 |
Jun 26, 2015 |
|
|
|
62191853 |
Jul 13, 2015 |
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Current U.S.
Class: |
136/247 |
Current CPC
Class: |
C09K 11/881 20130101;
H01L 31/0547 20141201; Y10S 977/948 20130101; H01L 31/0468
20141201; H01L 31/055 20130101; C03C 2217/445 20130101; C08K 9/10
20130101; C08K 2201/011 20130101; C03C 17/009 20130101; Y10S
977/774 20130101; Y02E 10/52 20130101; C09K 11/621 20130101; B82Y
30/00 20130101; C03C 2217/48 20130101; C08K 2201/001 20130101; C09D
7/62 20180101; Y10S 977/783 20130101; C08K 3/013 20180101; B82Y
20/00 20130101; C03C 2217/475 20130101; C09K 11/025 20130101; C08K
3/013 20180101; C08L 33/10 20130101 |
International
Class: |
H01L 31/0468 20060101
H01L031/0468; C09K 11/88 20060101 C09K011/88; H01L 31/055 20060101
H01L031/055; C09D 5/32 20060101 C09D005/32; C09D 7/12 20060101
C09D007/12; H01L 31/054 20060101 H01L031/054; C09K 11/02 20060101
C09K011/02; C09K 11/62 20060101 C09K011/62 |
Goverment Interests
ACKNOWLEDGMENT OF GOVERNMENT SUPPORT
[0002] This invention was made with government support under
Contract No. DE-AC52-06NA25396 awarded by the U.S. Department of
Energy. The government has certain rights in the invention.
Claims
1. A substantially transparent composition, comprising: a
transparent matrix; and plural, substantially non-aggregated heavy
metal free nanocrystals substantially homogeneously dispersed in
the transparent matrix and separated by a distance greater than an
energy transfer distance.
2. The composition of claim 1, wherein the heavy metal free
nanocrystals do not comprise cadmium, mercury, arsenic or lead.
3. The composition of claim 1, wherein the heavy metal free
nanocrystals comprise a core and at least one shell.
4. The composition of claim 3, wherein the shell comprises a shell
material and the shell material is selected to enhance the
stability of the core, to enable the nanocrystals to be dispersed
in a matrix without substantially quenching the quantum yield of
the nanocrystals, to maintain or improve the photoluminescent
intensity of the nanocrystal, or a combination thereof.
5. The composition of claim 1, wherein the transparent matrix is a
polymer matrix, sol-gel matrix, glass matrix, solvent matrix, or
combination thereof.
6. The composition of claim 5, wherein the transparent matrix is a
polymer matrix comprising a polymer selected from poly acrylate,
poly methacrylate, polyolefin, poly vinyl, epoxy resin,
polycarbonate, polyacetate, polyamide, polyurethane, polyketone,
polyester, polycyanoacrylate, silicone, polyglycol, polyimide,
fluorinated polymer, polycellulose, poly oxazine, or combinations
thereof.
7. The composition of claim 5, wherein the polymer matrix comprises
an acrylate polymer.
8. The composition of claim 7, wherein the acrylate polymer
comprises polylauryl methacrylate.
9. The composition of claim 1, wherein the nanocrystal comprises
zinc sulfide, zinc selenide, zinc oxide, zinc telluride, aluminum
nitride, aluminum sulfide, aluminum phosphide, aluminum antimonide,
gallium nitride, gallium phosphide, gallium antimonide, indium
nitride, indium phosphide, indium antimonide, thallium nitride,
thallium phosphide, thallium antimonide, indium gallium nitride,
indium gallium phosphide, aluminum indium nitride, indium aluminum
phosphide, aluminum gallium phosphide, aluminum indium gallium
nitride, silver indium selenide sulfide, gold indium selenide
sulfide, copper aluminum selenide sulfide, copper gallium selenide
sulfide, silver indium selenide, gold indium sulfide, copper
aluminum selenide, copper gallium selenide, copper indium selenide
sulfide, Si, Ge, Sn, SiGe, SiSn, GeSn, aluminum, gold, silver,
cobalt, iron, nickel, copper, gallium, silicon, manganese, indium,
selenium, sulfur or combinations thereof.
10. The composition of claim 1, wherein the nanocrystal has a
core/shell structure selected from InP/ZnSe, InSb/ZnSe, InP/ZnS,
InSb/ZnS, Ge/Si, Si/Ge, Sn/Si, Si/Sn, Ge/Sn, Sn/Ge,
AgInSe.sub.xS.sub.2-x/ZnS, AuInSe.sub.xS.sub.2-x/ZnS,
CuAlSe.sub.xS.sub.2-x/ZnS, CuGaSe.sub.xS.sub.2-x/ZnS,
CuInSe.sub.xS.sub.2-x/CuInS.sub.2,
CuInSe.sub.xS.sub.2-x/AuGaS.sub.2, or CuInSe.sub.xS.sub.2-x/ZnS,
where x is from 0 to 2.
11. The composition of claim 1, wherein a concentration of
nanocrystals in the transparent matrix is from greater than zero wt
% to 10 wt % relative to the weight of the transparent matrix.
12. The composition of claim 1, wherein the nanocrystals are
dispersed in the transparent matrix such than a nanocrystal
emission efficiency drops by less than 10% compared to a
nanocrystal emission efficiency of nanocrystals dissolved in a
solvent.
13. The composition of claim 1, wherein the composition has a color
rendering index of from 80 to 100, an optical power conversion
ratio of greater than 1%, absorbs at least 10% of incident solar
light, or a combination thereof.
14. The composition of claim 1, wherein the nanocrystals have a
core/shell structure of CuInSe.sub.xS.sub.2-x/ZnS, where x is from
greater than 0 to less than 2.
15. A composition substantially transparent to visible light, IR
light, UV light, or a combination thereof, the composition,
comprising: a polymer matrix wherein the polymer is selected from
poly acrylate, poly methacrylate, polyolefin, poly vinyl, epoxy
resin, polycarbonate, polyacetate, polyamide, polyurethane,
polyketone, polyester, polycyanoacrylate, silicone, polyglycol,
polyimide, fluorinated polymer, polycellulose, poly oxazine or
combinations thereof; and plural, substantially non-aggregated
heavy metal free nanocrystals substantially homogeneously dispersed
in the polymer matrix at a concentration of from greater than zero
wt % to 1 wt % relative to the weight of the polymer matrix such
that a nanocrystal emission efficiency drops by less than 10%
compared to a quantum dot emission efficiency of nanocrystals
dissolved in a solvent, the core/shell structure being selected
from InP/ZnSe, InSb/ZnSe, InP/ZnS, InSb/ZnS, Ge/Si, Si/Ge, Sn/Si,
Si/Sn, Ge/Sn, Sn/Ge, AgInSe.sub.xS.sub.2-x/ZnS,
AuInSe.sub.xS.sub.2-x/ZnS, CuAlSe.sub.xS.sub.2-x/ZnS,
CuGaSe.sub.xS.sub.2-x/ZnS, CuInSe.sub.xS.sub.2-x/CuInS.sub.2,
CuInSe.sub.xS.sub.2-x/AuGaS.sub.2, or CuInSe.sub.xS.sub.2-x/ZnS,
where x is from 0 to 2, the nanocrystals having a global Stokes
shift of greater than 200 meV and being separated by a distance
greater than an energy transfer distance; wherein the composition
has a color rendering index of from 90 to 100.
16. A device, comprising the composition of claim 1.
17. The device of claim 16, wherein the transparent matrix is a
matrix transparent or semi-transparent to visible light, infrared
light, ultraviolet light or a combination thereof.
18. The device of claim 16, comprising a transparent substrate at
least partially coated with a film comprising the composition.
19. The device of claim 18, wherein the transparent substrate is a
glass substrate.
20. The device of claim 16, further comprising a photovoltaic, a
reflector, a diffuser, or a combination thereof.
21. The device of claim 16, wherein the device is a window.
22. The device of claim 21, wherein the window comprises at least
one window pane comprising the composition, at least one window
pane at least partially coated with a film comprising the
composition, at least two window panes with the composition
positioned between the window panes, or a combination thereof.
23. The device of claim 16, wherein the nanocrystals have a
core/shell structure of CuInSe.sub.xS.sub.2-x/ZnS, where x is from
0 to 2.
24. The device of claim 16, wherein the device has a color
rendering index of from 80 to 100.
25. A method for making a composition, comprising: dispersing heavy
metal free nanocrystals in a first amount of a monomer and a first
polymerization initiator to form a dispersion of quantum dots in
monomer; mixing the dispersion of quantum dots in monomer with a
second amount of the monomer and an initiator to form a mixture;
agitating the mixture; and initiating polymerization of the monomer
to form the composition comprising a transparent matrix with
quantum dots dispersed within.
26. The method of claim 25, further comprising allowing the
polymerization to proceed in the dark.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of the earlier filing
dates of U.S. Provisional Application No. 62/185,414, filed on Jun.
26, 2015, and U.S. Provisional Application No. 62/191,853, filed on
Jul. 13, 2015. Each of these prior applications is incorporated
herein by reference.
FIELD
[0003] Certain disclosed embodiments concern a composition
comprising heavy metal free semiconductor nanocrystals either
dispersed in a transparent matrix, or applied as a coating, and a
device and method for using the composition, such as a luminescence
solar concentrator.
BACKGROUND
[0004] In the near future, building integrated photovoltaics (PV)
could revolutionize urban architecture by allowing one to reach the
ambitious goal of net zero energy consumption buildings.
Luminescent solar concentrators (LSCs) can play an important role
in this transition. For example, semi-transparent PV windows
comprising LSCs could convert the energy passive facades of urban
buildings into distributed energy generation units.
[0005] However, despite their large promise, wide use of LSCs has
so far been hindered by the lack of suitable emitters. Typically
used conjugated organic and organo-metallic fluorophores provide a
limited coverage of the solar spectrum and suffer from significant
optical losses associated with re-absorption of guided
luminescence. For example,
4-dicyanomethyl-6-dimethylaminostiryl-4H-pyran (DCM), a large
Stokes shift red-emitting LSC dye, has absorption onset at about
470 nm and thus does not harvest a significant fraction of the
solar spectrum. The same limitation affects Europium organic
complexes that emit at about 610 nm. Despite having completely
suppressed self-absorption, they exhibit absorption spectra that
are limited to the blue-green spectral region. Even top performing
organic dyes such as BASF Lumogen RED, still exhibit a significant
overlap between their absorption and emission spectra, leading to
considerable losses to re-absorption over relatively short optical
distances. These deficiencies reduce the light harvesting
efficiency of LSCs and also lead to strong coloring of devices,
which imposes certain constrains on their usage in
architecture.
SUMMARY
[0006] Disclosed herein are embodiments of a substantially
transparent composition. In some embodiments, the composition
comprises a transparent matrix and plural, substantially
non-aggregated heavy metal free nanocrystals substantially
homogeneously dispersed in the transparent matrix and separated by
a distance greater than an energy transfer distance. The
transparent matrix may be a polymer matrix, a glass matrix, a
sol-gel matrix, a solvent matrix or a combination thereof. In
certain embodiments, the transparent matrix is a polymer matrix. In
some embodiments, the transparent matrix stands on its own, in
others the matrix is applied as a coating on a typical window
material, such as on glass. In some embodiments, the heavy metal
free nanocrystals do not comprise cadmium, and additionally, may
not comprise mercury, arsenic or lead. The nanocrystals may have a
shape selected from a sphere, rod, tetrapod, heteronanorod,
hetero-platelet, hetero-tripod, hetero-tetrapod, hetero-hexapod,
dot-in-rod, dot-in-platelet, rod-in-rod and platelet-in-platelet,
dot-in-bulk, complex branched hetero-structure, or a combination
thereof.
[0007] The nanocrystals may comprise a core and at least one shell.
The nanocrystal core may have an intrinsically large Stokes shift,
and the shell may not substantially affect the Stokes shift of the
nanocrystal. The shell may comprise a shell material selected to
enhance the stability of the core, to enable the nanocrystals to be
dispersed in a matrix without substantially quenching the
photoluminescence quantum yield of the nanocrystals, maintain or
improve the photoluminescent intensity of the nanocrystal or a
combination thereof.
[0008] The nanocrystal may comprise InSb, InP, Ge, Si, Sn, Sn, InN,
AlN, GaN, ZnTe, ZnSe, ZnS, ZnO, AgInSe.sub.xS.sub.2-x,
AuInSe.sub.xS.sub.2-x, CuAlSe.sub.xS.sub.2-x,
CuGaSe.sub.xS.sub.2-x, or CuInSe.sub.xS.sub.2-x, where x is from 0
to 2, or from greater than 0 to less than 2, or combinations
thereof. The nanocrystal may have a core comprising InSb, InP, Ge,
Si, Sn, Sn, InN, AlN, GaN, ZnTe, ZnSe, ZnS, ZnO,
AgInSe.sub.xS.sub.2-x, AuInSe.sub.xS.sub.2-x,
CuAlSe.sub.xS.sub.2-x, CuGaSe.sub.xS.sub.2-x,
CuInSe.sub.xS.sub.2-x, or combinations thereof, and/or a shell
comprising InSb, InP, Ge, Si, Sn, Sn, InN, AlN, GaN, ZnTe, ZnSe,
ZnS, ZnO, AgInSe.sub.xS.sub.2-x, AuInSe.sub.xS.sub.2-x,
CuAlSe.sub.xS.sub.2-x, CuGaSe.sub.xS.sub.2-x, or combinations
thereof. In some embodiments, the nanocrystal has a core/shell
structure selected from InP/ZnSe, InSb/ZnSe, InP/ZnS, InSb/ZnS,
Ge/Si, Si/Ge, Sn/Si, Si/Sn, Ge/Sn, Sn/Ge,
AgInSe.sub.xS.sub.2-x/ZnS, AuInSe.sub.xS.sub.2-x/ZnS,
CuAlSe.sub.xS.sub.2-x/ZnS, CuGaSe.sub.xS.sub.2-x/ZnS,
CuInSe.sub.xS.sub.2-x/CuInS.sub.2,
CuInSe.sub.xS.sub.2-x/AuGaS.sub.2, or CuInSe.sub.xS.sub.2-x/ZnS,
where x is from 0 to 2, or from greater than 0 to less than 2.
[0009] The nanocrystal concentration in the transparent matrix may
be from greater than zero wt % to 10 wt % relative to the weight of
the transparent matrix, such as from greater than zero wt % to 0.5
wt %, or from 0.1 wt % to 0.2 wt %. The nanocrystals may be
dispersed in the transparent matrix such that a nanocrystal
emission efficiency drops by less than 10% compared to a emission
efficiency of nanocrystals dissolved in a solvent, such as by less
than 5%, by less than 1%, or approximately 0%.
[0010] The composition may comprise a transparent matrix that is
substantially transparent to visible light, infrared (IR) light,
ultraviolet (UV) light, or a combination thereof. The transparent
matrix may be an acrylate polymer, such as polylauryl methacrylate.
The composition may be substantially colorless, and in some
embodiments, the composition has a color rendering index of from 80
to 100, such as from 90 to 100. The composition may absorb at least
10% of incident solar light, and/or may have an optical power
conversion ratio of greater than 1%. In some embodiments, the
composition has a Stokes shift of greater than 200 meV.
[0011] Also disclosed are embodiments of a device comprising the
disclosed composition. The device may comprise a polymer matrix
comprising the nanocrystals. Alternatively, or additionally, the
device may comprise a transparent substrate at least partially
covered with a film comprising the composition. The transparent
substrate may be a glass substrate. The device may comprise a
photovoltaic, a reflector, a diffuser or a combination thereof. The
device may be a window, and may comprise at least one window pane
comprising the disclosed composition. In some embodiments, the
window comprises at least one window pane at least partially coated
with a film comprising the composition, and/or may comprise at
least two window panes with the composition positioned between the
window panes.
[0012] A building or transportation device having at least one
window comprising the composition is also disclosed. The
transportation device may be an automobile, ship or airplane.
[0013] Embodiments of a method for making the composition are also
disclosed. In some embodiments, the method comprises dispersing
heavy metal free nanocrystals in a first amount of a monomer and a
first polymerization initiator to form a dispersion of quantum dots
in monomer and mixing the dispersion of quantum dots in monomer
with a second amount of the monomer and an initiator to form a
mixture. The mixture is then agitated, such as by stirring,
sonicating, shaking, or a combination thereof, and polymerization
of the monomer is initiated to form the composition comprising a
transparent matrix with quantum dots dispersed within. The
polymerization may proceed in the dark. The initiator may be a
radical initiator and initiating polymerization may comprise
irradiating the mixture with light. In some embodiments, the
initiator is 2,2-dimethoxy-1,2-diphenylethan-1-one. The mixture may
also comprise a cross-linking agent, which may comprise ethylene
glycol dimethacrylate.
[0014] The foregoing and other objects, features, and advantages of
the invention will become more apparent from the following detailed
description, which proceeds with reference to the accompanying
figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The patent or application file contains at least one drawing
executed in color. Copies of this patent or patent application
publication with color drawing(s) will be provided by the Office
upon request and payment of the necessary fee.
[0016] FIG. 1 is a schematic representation of an exemplary neutral
density LSC comprising a polymer matrix incorporating ZnS-coated
CISeS quantum dots (QDs).
[0017] FIG. 2A provides the optical absorption and
photoluminescence spectra of
4-dicyanomethyl-6-dimethylaminostiryl-4H-pyran (DCM) dye.
[0018] FIG. 2B provides the optical absorption and
photoluminescence spectra of BASF Lumogen red dye.
[0019] FIG. 2C provides the optical absorption and
photoluminescence spectra of europium tris(2-thenoyl trifluoro
acetonate)-di(triphenylphosphine oxide) (Eu(TTA).sub.3(TPPO).sub.2)
dye.
[0020] FIG. 2D provides the optical absorption and
photoluminescence spectra of yellow emitting Crs040 Dye from
Radiant Color.
[0021] FIG. 2E provides the optical absorption and
photoluminescence spectra of a perylene perinone dye.
[0022] FIG. 2F provides the optical absorption and
photoluminescence spectra of CdSe/CdS core shell hetero-QD (shell
comprises 14 CdS monolayers).
[0023] FIG. 3 is a schematic diagram illustrating some exemplary
alternative geometries of hetero-structured nanocrystals.
[0024] FIG. 4 is a schematic diagram of one embodiment of a
luminescent solar concentrator.
[0025] FIG. 5 is a plot of differential scanning calorimetry (DSC)
curves of the pure polymer (LSC0) and CISeS QDs/P(LMA-co-EGDM)
nanocomposites (LSC10 and LSC20).
[0026] FIG. 6 provides plots of weight loss versus temperature,
illustrating the TGA (Thermo-gravimetric) and DTA (differential
thermo-gravimetric) curves of the pure polymer (LSC0) and CISeS
QDs/P(LMA-co-EGDM) nanocomposites (LSC10 and LSC20).
[0027] FIG. 7 is a plot illustrating the absorption,
photoluminescence (PL), external quantum efficiency (EQE) and solar
(grey shading) spectra versus wavelength.
[0028] FIG. 8A is a schematic representation of a cell casting
procedure used for the fabrication of a quantum dot luminescent
solar concentrator (QD-LSC).
[0029] FIG. 8B is a photograph of an LSC comprising 0.3 wt % of the
QDs under ambient illumination.
[0030] FIG. 9 is a plot of absorbance (dashed lines) and
photoluminescence (solid lines) versus wavelength, illustrating the
absorbance and photoluminescence of the QDs in toluene (black) and
in a polymer (PLMA) matrix (red).
[0031] FIG. 10 is a plot of photoluminescence versus time,
illustrating the photoluminescence decays measured using weak
pulsed 405 nm excitation of ZnS-coated CISeS QDs in different
environments.
[0032] FIG. 11 is a plot of photoluminescence versus time,
illustrating the room temperature photoluminescence decay of CISeS
QDs with no further ZnS passivation in toluene (black) and PLMA
(red).
[0033] FIG. 12 is a photograph taken with a UV-filtered IR camera
of a disclosed luminescent solar concentrator comprising 0.3 wt %
of ZnS-coated CISeS QDs under UV illumination.
[0034] FIG. 13 is a plot of absorbance and photoluminescence versus
wavelength, illustrating the photoluminescence collected at the
edge of the LSC when the excitation spot was located at various
distances from the edge.
[0035] FIG. 14 is a plot of photoluminescence versus optical
distance, illustrating the photoluminescence output as a function
of distance.
[0036] FIG. 15 provides examples of photon trajectories obtained
from Monte Carlo ray tracing simulations.
[0037] FIG. 16 is a schematic representation of the relative
probabilities for re-emitted photons to reach an LSC edge.
[0038] FIG. 17A provides Monte Carlo ray tracing simulations of
photon output probability in comparison to the probability of
non-radiative decay and photon escape through the device surfaces
for the LSCs from FIGS. 12-16, considering QDs with
photoluminescence quantum yields of 40%.
[0039] FIG. 17B provides Monte Carlo ray tracing simulations of
photon output probability in comparison to the probability of
non-radiative decay and photon escape through the device surfaces
for the LSCs from FIGS. 12-16, considering QDs with
photoluminescence quantum yields of 100%.
[0040] FIG. 18 is a photograph of a ZnS-coated CISeS QD LSC during
optical power conversion efficiency measurements with illumination
from a solar simulator (1.5 AM Global), and an inset showing the
photograph of the same device taken with an IR camera.
[0041] FIG. 19 is a photograph of a large area LSC with dimensions
12 cm.times.12 cm.times.0.3 cm comprising 0.3 wt % QDs that absorbs
approximately 10% of spectrally integrated incident radiation
(LSC10).
[0042] FIG. 20 is a photograph of a large area LSC with dimensions
12 cm.times.12 cm.times.0.3 cm comprising 0.5 wt % QDs that absorbs
approximately 20% of spectrally integrated incident radiation
(LSC20).
[0043] FIG. 21A is a photograph of a colorful scene taken with a
Canon EOS 400D camera without using any filters.
[0044] FIG. 21B is a photograph of a colorful scene taken with a
Canon EOS 400D camera with an LSC10 placed in front of the camera
lens.
[0045] FIG. 21C is a photograph of a colorful scene taken with a
Canon EOS 400D camera with an LSC20 placed in front of the camera
lens.
[0046] FIG. 22A is a photograph of a reflecting white background
taken with half of the field of view filtered with LSC10.
[0047] FIG. 22B is a photograph of a reflecting white background
taken with the same camera as FIG. 22A with half of the field of
view filtered with LSC20.
[0048] FIG. 23A is a photograph of an LSC (12 cm.times.3.5
cm.times.0.3 cm) incorporating Crs040 Yellow dye.
[0049] FIG. 23B is a photograph of a reflecting white background
taken with the same camera as used in FIG. 23A with half of the
field of view filtered with the Crs040-LSC.
[0050] FIG. 23C is a color rendering index (CRI) plot of original
Munsell test color samples (TCS) under D65 reference illuminant
before (white circles) and after chromatic adaptation by the
Crs040-LSC (yellow circles).
[0051] FIG. 24 is a CIE L*a*b* (Commission Internationale de le
{tilde over (E)}clairage) representation of the color space of the
LSC20 and Crs040-LSC.
[0052] FIG. 25 is a plot of reflectivity versus wavelength,
illustrating the reflectance of LSC20 and the LSC incorporating
Crs040 Yellow dye. These data are collected using an integrating
sphere and placing a Spectralon.RTM. scatterer on the back side of
the LSCs.
[0053] FIG. 26 is a plot illustrating the color coordinates (CIE
1960 Uniform Color Space) of original Munsell test color samples
(TCS) under D65 reference illuminant both unfiltered (white
circles) and with spectral filtering by LSC20 (brown circles).
[0054] FIG. 27 is a plot of total error score versus subject
number, illustrating the results from a Farnsworth-Munsell 100 hue
color vision test.
[0055] FIG. 28 is a plot of photoluminescence (solid black),
absorption (solid red) and photoluminescence excitation (PLE;
dashed grey) spectra versus wavelength for 2 nm CIS QDs. In the
case of photoluminescence measurements, the QDs are excited at 400
nm (3.1 eV).
[0056] FIG. 29 is a plot of PL intensity versus photoexcitation
wavelength, illustrating the photoluminescence excitation spectra
(arbitrary units) of 2 nm CIS QDs collected with 2.5 nm bandwidth
at 555 nm, 600 nm and 655 nm.
[0057] FIG. 30 is a TA spectra of the QDs from FIG. 28, measured at
different delays after excitation.
[0058] FIG. 31 is a plot illustrating the pump-intensity dependence
of TA decay in CIS QDs measured at 500 nm (2.48 eV).
DETAILED DESCRIPTION
I. Definitions
[0059] The following explanations of terms and methods are provided
to better describe the present disclosure and to guide those of
ordinary skill in the art in the practice of the present
disclosure. The singular forms "a," "an," and "the" refer to one or
more than one, unless the context clearly dictates otherwise. The
term "or" refers to a single element of stated alternative elements
or a combination of two or more elements, unless the context
clearly indicates otherwise. As used herein, "comprises" means
"includes." Thus, "comprising A or B," means "including A, B, or A
and B," without excluding additional elements. All references,
including patents and patent applications cited herein, are
incorporated by reference.
[0060] Unless otherwise indicated, all numbers expressing
quantities of components, molecular weights, percentages,
temperatures, times, and so forth, as used in the specification or
claims are to be understood as being modified by the term "about."
Accordingly, unless otherwise indicated, implicitly or explicitly,
the numerical parameters set forth are approximations that may
depend on the desired properties sought and/or limits of detection
under standard test conditions/methods. When directly and
explicitly distinguishing embodiments from discussed prior art, the
embodiment numbers are not approximates unless the word "about" is
recited.
[0061] Unless explained otherwise, all technical and scientific
terms used herein have the same meaning as commonly understood to
one of ordinary skill in the art to which this disclosure belongs.
Although methods and materials similar or equivalent to those
described herein can be used in the practice or testing of the
present disclosure, suitable methods and materials are described
below. The materials, methods, and examples are illustrative only
and not intended to be limiting.
[0062] As used herein, "heavy metal" refers to toxic elements
selected from the group consisting of arsenic, cadmium, lead, and
mercury.
[0063] As used herein, "alkyl" refers to a straight (i.e.,
unbranched), branched or cyclic saturated hydrocarbon chain. Unless
expressly stated otherwise, an alkyl group contains from one to at
least twenty-five carbon atoms (C.sub.1-C.sub.25); for example,
from one to fifteen (C.sub.1-C.sub.15), from one to ten
(C.sub.1-C.sub.10), from one to six (C.sub.1-C.sub.6), or from one
to four (C.sub.1-C.sub.4) carbon atoms. A cycloalkyl contains from
three to at least twenty-five carbon atoms (C.sub.1-C.sub.25); for
example, from three to fifteen (C.sub.1-C.sub.15), from three to
ten (C.sub.1-C.sub.10), from three to six (C.sub.1-C.sub.6). The
term "lower alkyl" refers to an alkyl group comprising from one to
ten carbon atoms or three to ten for a cycloalkyl. Unless expressly
referred to as "unsubstituted alkyl," an alkyl group can either be
substituted or unsubstituted. Examples of alkyl groups include, but
are not limited to, groups such as methyl, ethyl, n-propyl,
isopropyl, n-butyl, t-butyl, isobutyl, sec-butyl, homologs and
isomers of, for example, n-pentyl, n-hexyl, n-heptyl, n-octyl,
n-nonyl, n-decyl, n-dodecyl (lauryl) and the like. Examples of
cycloalkyl groups include, but are not limited to, cyclopropyl,
cyclobutyl, cyclopentyl, cyclohexyl and the like.
II. Overview
[0064] An LSC typically comprises a glass or plastic waveguide
coated or doped with highly emissive fluorophores. Direct and
diffused sunlight is absorbed by a fluorophore and re-emitted at a
longer wavelength. The luminescence propagates to the waveguide
edges by total internal reflection and is converted into
electricity by high-efficiency PV cells installed along the slab
perimeter (FIG. 1). Since the surface of the slab exposed to
sunlight can be much larger than the surface of its edges, the LSC
effectively increases the photon density incident onto the PV cell,
which can boost its photocurrent. In FIG. 1 a simplified structure
of band-edge electronic states in CISeS QDs responsible for light
emission and absorption is illustrated. Light absorption is
dominated by optical transitions involving intrinsic quantized
states (the band-edge transition is shown by the arrow from VB to
CB) while emission involves a band-edge electron state and an
intra-gap hole state (CB to D arrow), which results in a large
Stokes shift.
[0065] By matching the emission wavelength of active chromophores
to the spectral peak of the external quantum efficiency (EQE), a
further increase in the power output of the PV devices can be
achieved. The color and the degree of transparency of an LSC, which
are defined by the type and the concentration of the fluorophores,
can be selected according to specific building requirements and/or
aesthetic criteria.
[0066] Conjugated organic and organo-metallic fluorophores
typically provide a limited coverage of the solar spectrum and
often suffer from significant optical losses associated with
re-absorption of guided luminescence. And organic dyes such as BASF
Lumogen RED still exhibit significant losses to re-absorption over
relatively short optical distances, possibly due to the significant
overlap between their absorption and emission spectra (FIGS.
2A-2F). Colloidal or nanocrystal quantum dots (QDs) can help
overcome these limitations. Colloidal or nanocrystal quantum dots
feature near unity photoluminescence (PL) quantum yields
(.PHI..sub.PL) and narrow, widely tunable emission spectra that can
be readily matched to various solar cells including both single-
and multi-junction devices. Optimization of .PHI..sub.PL alone is
however insufficient for realizing highly efficient LSCs. Another
advantageous parameter of LSC fluorophores is the spectral overlap
between the emission peak and the absorption spectrum. It
determines the magnitude of intrinsic optical losses in devices as
attenuation of re-emitted radiation occurs primarily due to
"randomization" of the direction of propagating photons and thus
increased losses through the "escape" cone following each
re-absorption/reemission event. This ultimately results in strong
device-size dependence of the LSC optical efficiency.
[0067] An attractive feature of the QDs is that they can be
engineered to provide a large Stokes shift. A large Stokes shift
can result in a large reduction in the overlap between optical
absorption and emission spectra, which can be useful in the
realization of large area LSCs with suppressed re-absorption
losses. Recently, several strategies for increasing Stokes shift
have been demonstrated in the literature. One approach involves the
use of thick-shell CdSe/CdS QDs in which a large-volume CdS shell
serves as a light-harvesting antenna while a core of a narrower gap
CdSe as a lower-energy emitter. These structures exhibit a wide
spectral separation between the absorption onset and the emission
spectrum (about 400 meV) which allowed for the realization of
prototype large-area LSCs with no re-absorption losses over
distances of tens of centimeters. A similarly large Stokes shift
can be obtained using other types of CdSe/CdS heterostructures such
as CdSe/CdS seeded nanorods that were used to demonstrate direct
integration of ultrathin, transfer-printed Si solar cells into an
LCS. Another strategy for obtaining a large Stokes shift utilizes
doping of QDs with transition metal ions that act as intragap
radiative recombination centers excited via light absorption in the
semiconductor host. And re-absorption-free transparent QD-LSCs were
recently fabricated using Mn-doped ZnSe QDs.
[0068] However, despite their great potential, LSCs fabricated
using CdSe/CdS heterostructures or doped ZnSe QDs suffer from
incomplete coverage of the solar spectrum due to a large energy gap
of the absorber material (2.46 eV for CdS and 2.7 for ZnSe) that
may also lead to strong coloring of devices. In the case of
core/shell structures, this problem could potentially be mitigated
by employing recently demonstrated giant-shell PbSe/CdSe QDs that
feature a lowered absorption onset (about 1.75 eV) and
near-infrared (IR) luminescence characterized by a large effective
Stokes shift. These structures, however, contain hazardous heavy
metal ions and thus require expensive disposal/recycling protocols,
a problem which is similar to one encountered with CdSe/CdS
nanocrystals.
[0069] The compositions disclosed herein comprise heavy metal-free
QDs that provide a large, hundreds of meV Stokes shift without the
need for heterostructuring. These QDs are ternary I-III-VI.sub.2
semiconductors such as CuInS.sub.2 (CIS), CuInSe.sub.2 (CISe), and
their alloys (CuInSe.sub.xS.sub.2-x or CISeS). Another attractive
feature of these QDs is that they can be fabricated in large
quantities via high-throughput, non-injection techniques using
inexpensive precursors. Furthermore, their large absorption
cross-sections and a spectrally tunable, near-IR absorption onset
are well suited for harvesting solar radiation. Recently, ternary
I-III-VI.sub.2 QDs have been used to demonstrate high-efficiency
QD-sensitized solar cells, which exemplefies how low-toxicity
alternatives can outperform toxic QDs. They are also highly
efficient, tunable emitters and their PL quantum yields can be
pushed to above 80% using surface treatment with Cd.sup.2+ ions or
inorganic passivation with an outer shell of wide-gap ZnS.
III. Composition
[0070] Disclosed herein are embodiments of a composition comprising
a transparent matrix and a plurality of semiconductor nanocrystals.
In some embodiments, the composition is at least partially
transparent to light, such as visible light, infrared (IR) light,
ultraviolet (UV) light or combinations thereof, and may be
substantially transparent to the light. The transparent matrix can
be any matrix suitable to disperse the nanocrystals, and may be a
polymer matrix, a glass matrix, a sol-gel matrix, a solvent matrix
or a combination thereof.
[0071] A. Heavy Metal Free Semiconductor Nanocrystals
[0072] Semiconductor nanocrystals are crystalline particles of
different shapes (spheres, cubes, rods, plates, branched structures
such as tripods and tetrapods, etc.) that are sufficiently small to
exhibit quantum mechanical properties. Nanocrystals may have
different shapes including almost spherical particles (often
referred to as "quantum dots" or "QDs"), elongated particles (known
as "nanorods" or "quantum rods"), two-dimensional nanoplatelets, or
complex branched structures such as tripods, tetrapods, pentapods,
etc. The nanocrystals may comprise more than one semiconductor
material. The nanocrystals may be heavy metal free nanocrystals. In
some examples, heavy metal free nanocrystals do not comprise toxic
heavy metals. In some embodiments, heavy metal free nanocrystals do
not comprise cadmium. In other embodiments, heavy metal free
nanocrystals do not comprise cadmium, mercury, arsenic or lead.
[0073] In some embodiments, the nanocrystals are colloidal
nanocrystals. The nanocrystals may comprise a core and one or more
shells enclosing the core. In alternative embodiments, the
nanocrystals do not comprise a shell enclosing the core. The core
and optional one or more shells may be made from the same or
different materials. In certain embodiments, the nanocrystals
comprise a core comprising a core material and a shell comprising a
shell material. In some examples, the quantum dots further comprise
at least a second shell comprising the same shell material or a
second shell material. The core and optional shell(s) materials can
be selected so as to produce quantum dots with specifically desired
properties, such as a global Stokes-shift in a particular desired
range, such as greater than 50 meV, greater than 100 meV, greater
than 200 meV, greater than 300 meV, or greater than 400 meV.
[0074] In some embodiments, the core has an intrinsically large
Stokes shift, such as a Stokes shift in the desired range, and the
presence of the shell material, if present, does not substantially
affect the Stokes shift of the nanocrystal. In certain embodiments,
the nanocrystal comprises one or more shells comprising shell
materials selected to enhance the stability of the core, to enable
the nanocrystals to be dispersed in a matrix without substantially
quenching the quantum yield of the nanocrystals, maintain or
improve the photoluminescent intensity of the nanocrystal or a
combination thereof.
[0075] In some embodiments, the colloidal nanocrystals include a
core of a binary semiconductor material, e.g., a core of the
formula MX, where M can be zinc, aluminum, tin, gallium, indium,
thallium, magnesium, calcium, strontium, barium, copper, and
mixtures or alloys thereof and X is sulfur, selenium, tellurium,
nitrogen, phosphorus, antimony, and mixtures or alloys thereof. In
other embodiments, the colloidal quantum dots include a core of a
ternary semiconductor material, e.g., a core of the formula
M.sub.1M.sub.2X, where M.sub.1 and M.sub.2 can be zinc, aluminum,
tin, gallium, indium, thallium, magnesium, calcium, strontium,
barium, copper, and mixtures or alloys thereof and X is sulfur,
selenium, tellurium, nitrogen, phosphorus, antimony, and mixtures
or alloys thereof. In alternative embodiments, the colloidal
quantum dots include a core of a quaternary semiconductor material,
e.g., a core of the formula M.sub.1M.sub.2M.sub.3X, where M.sub.1,
M.sub.2 and M.sub.3 can be zinc, aluminum, tin, gallium, indium,
thallium, magnesium, calcium, strontium, barium, copper, and
mixtures or alloys thereof and X is sulfur, selenium, tellurium,
nitrogen, phosphorus, antimony, and mixtures or alloys thereof. In
other examples, the colloidal quantum dots include a core of a
quaternary semiconductor material, e.g., a core of a formula such
as M.sub.1X.sub.1X.sub.2, M.sub.1M.sub.2X.sub.1X.sub.2,
M.sub.1M.sub.2M.sub.3X.sub.1X.sub.2, M.sub.1X.sub.1X.sub.2X.sub.3,
M.sub.1M.sub.2X.sub.1X.sub.2X.sub.3 or
M.sub.1M.sub.2M.sub.3X.sub.1X.sub.2X.sub.3, where M.sub.1, M.sub.2
and M.sub.3 can be zinc, aluminum, tin, gallium, indium, thallium,
magnesium, calcium, strontium, barium, copper, and mixtures or
alloys thereof and X.sub.1, X.sub.2 and X.sub.3 can be sulfur,
selenium, tellurium, nitrogen, phosphorus, antimony, and mixtures
or alloys thereof. Examples include zinc sulfide (ZnS), zinc
selenide (ZnSe), zinc telluride (ZnTe), aluminum nitride (AlN),
aluminum sulfide (AlS), aluminum phosphide (AlP), aluminum
antimonide (AlSb), gallium nitride (GaN), gallium phosphide (GaP),
gallium antimonide (GaSb), indium nitride (InN), indium phosphide
(InP), indium antimonide (InSb), thallium nitride (TlN), thallium
phosphide (TlP), thallium antimonide (TlSb), indium gallium nitride
(InGaN), indium gallium phosphide (InGaP), aluminum indium nitride
(AlInN), indium aluminum phosphide (InAlP), aluminum gallium
phosphide (AlGaP), aluminum indium gallium nitride (AlInGaN),
silver indium selenide (AgInSe.sub.2), gold indium sulfide
(AuInS.sub.2), copper aluminum selenide (CuAlSe.sub.2), copper
gallium selenide (CuGaSe.sub.2), silver indium selenide sulfide
(AgInSe.sub.xS.sub.2-x), gold indium selenide sulfide
(AuInSe.sub.xS.sub.2-x), copper aluminum selenide sulfide
(CuAlSe.sub.xS.sub.2-x), copper gallium selenide sulfide
(CuGaSe.sub.xS.sub.2-x), copper indium selenide sulfide (CuInSeS),
copper indium selenide (CuInSe.sub.2), copper indium sulfide
(CuInS.sub.2) and the like, mixtures of such materials, or any
other semiconductor or similar materials. The colloidal nanocrystal
cores may be of silicon (Si), germanium (Ge), tin (Sn), and alloys
thereof (e.g., Sn.sub.xSi.sub.1-x, Sn.sub.xGe.sub.1-x, or
Ge.sub.xSi.sub.1-x, where x is from greater than 0 to less than 1),
or may be oxides such as zinc oxide (ZnO), titanium oxide
(TiO.sub.2), silicon oxide (SiO.sub.2), aluminum oxide
(Al.sub.2O.sub.3), or zirconium oxide (ZrO.sub.2) and the like. In
another embodiment, the colloidal nanocrystal include a core of a
metallic material such as gold (Au), silver (Ag), cobalt (Co), iron
(Fe), nickel (Ni), copper (Cu), manganese (Mn), alloys thereof and
alloy combinations. In other embodiments, the nanocrystal core
comprises copper, indium, selenium, sulfur or combinations thereof.
In certain embodiments, the nanocrystal core has a formula
CuInSe.sub.xS.sub.2-x, where x is from 0 to 2, such as CuInS.sub.2,
CuInSe.sub.0.1S.sub.1.9, CuInSe.sub.0.2S.sub.1.8,
CuInSe.sub.0.25S.sub.1.75, CuInSe.sub.0.3S.sub.1.7,
CuInSe.sub.0.4S.sub.1.6, CuInSe.sub.0.5S.sub.1.5,
CuInSe.sub.0.6S.sub.1.4, CuInSe.sub.0.7S.sub.1.3,
CuInSe.sub.0.75S.sub.1.25, CuInSe.sub.0.8S.sub.1.2,
CuInSe.sub.0.9S.sub.1.1, CuInSeS, CuInSe.sub.1.1S.sub.0.9,
CuInSe.sub.1.2S.sub.0.8, CuInSe.sub.1.25S.sub.0.75,
CuInSe.sub.1.3S.sub.0.7, CuInSe.sub.1.4S.sub.0.6,
CuInSe.sub.1.5S.sub.0.5, CuInSe.sub.1.6S.sub.0.4,
CuInSe.sub.1.7S.sub.0.3, CuInSe.sub.1.75S.sub.0.25,
CuInSe.sub.1.8S.sub.0.2, CuInSe.sub.1.9S.sub.0.1, CuInSe.sub.2 or a
combination thereof. In certain embodiments, x is from greater than
0 to less than 2.
[0076] Additionally, the nanocrystals may comprise one or more
shells about the core. The shells can also be a semiconductor
material, and may have a composition different than the composition
of the core. The shells can include materials selected from among
Group II-VI compounds, Group II-V compounds, Group III-VI
compounds, Group III-V compounds, Group IV-VI compounds, Group
compounds, Group I--II-IV-VI compounds, Group I-II-III-VI, and
Group IV compounds. Examples include zinc sulfide (ZnS), zinc
selenide (ZnSe), zinc telluride (ZnTe), aluminum nitride (AlN),
aluminum phosphide (AlP), aluminum antimonide (AlSb), gallium
nitride (GaN), gallium phosphide (GaP), gallium antimonide (GaSb),
indium nitride (InN), indium phosphide (InP), indium antimonide
(InSb), thallium nitride (TlN), thallium phosphide (TlP), thallium
antimonide (TlSb), zinc indium gallium nitride (InGaN), indium
gallium phosphide (InGaP), aluminum indium nitride (AlInN), indium
aluminum phosphide (InAlP), aluminum gallium phosphide (AlGaP),
aluminum indium gallium nitride (AlInGaN), silicon and the like,
mixtures of such materials, or any other semiconductor or similar
materials.
[0077] In certain embodiments, the nanocrystals comprise InSb, InP,
Ge, Si, Sn, Sn, InN, AlN, GaN, ZnTe, ZnSe, ZnS, ZnO or
CuInSe.sub.xS.sub.2-x, where x is from 0 to 2, such as from greater
than zero to less than 2. In some examples, the core material is
InSb, InP, Ge, Si, Sn, Sn, InN, AlN, GaN, ZnTe, ZnSe, ZnS, ZnO,
CuInSe.sub.xS.sub.2-x, where x is from 0 to 2, such as from greater
than zero to less than 2, or combinations thereof, and the shell
material is InSb, InP, Ge, Si, Sn, Sn, InN, AlN, GaN, ZnTe, ZnSe,
ZnS, or ZnO or combinations thereof. In certain embodiments, the
quantum dot has a core/shell structure selected from InP/ZnSe,
InSb/ZnSe, InP/ZnS, InSb/ZnS, Ge/Si, Si/Ge, Sn/Si, Si/Sn, Ge/Sn,
Sn/Ge, AgInSe.sub.xS.sub.2-x/ZnS, AuInSe.sub.xS.sub.2-x/ZnS,
CuAlSe.sub.xS.sub.2-x/ZnS, CuGaSe.sub.xS.sub.2-x/ZnS,
CuInSe.sub.xS.sub.2-x/CuInS.sub.2,
CuInSe.sub.xS.sub.2-x/AuGaS.sub.2, or CuInSe.sub.xS.sub.2-x/ZnS,
where x is from 0 to 2, or from greater than 0 to less than 2.
[0078] In some embodiments, the nanocrystals may comprise one
shell, but in other embodiments, the nanocrystals comprise more
than one shell, such as from 2 to 6 shells, or 2, 3, 4, 5 or 6
shells. Multiple shells can allow for additional tuning of the
properties of the nanocrystal. Adjacent shells may be of differing
materials.
[0079] The size of the shell in relation to the core can also be
selected to enhance or decrease certain properties of the
nanocrystal. The core may be small relative to the size of the
shell, and the shell thick may be relative to the core. In some
embodiments, the core has a radius of from 0.5 nm to 3 nm, such as
from 1 nm to 2 nm. In certain embodiments, the core has a radius of
1.5 nm. The shell thickness is measured from the outer surface of
the core to the outer surface of the nanocrystal. In some examples,
the shell has a thickness of from greater than 0 nm to greater than
10 nm, such as from 0.5 nm to 8 nm, from 2 nm to 7 nm or from 3 nm
to 6 nm.
[0080] In some embodiments, the nanocrystals are substantially
spherical and in this case are often referred to as quantum dots,
such as core/shell quantum dots. In other embodiments, the
nanocrystals have different shapes, such as rods, tetrapods,
heteronanorod, hetero-platelet, hetero-tripod, hetero-tetrapod,
hetero-hexapod, dot-in-rod, dot-in-platelet, rod-in-rod and
platelet-in-platelet, dot-in-bulk, complex branched
heterostructures or more complex geometries (see FIG. 3 for some
exemplary geometries). Further information regarding other possible
geometries for heterostructured quantum dots can be found in C. d.
M. Donega, Synthesis and properties of colloidal
heteronanocrystals, Chemical Society Reviews, 2011, 40:1512-1546,
which is incorporated herein by reference.
[0081] The nanocrystals can be made by any suitable method. One
exemplary method can be found in McDaniel, H. et al., Simple yet
versatile synthesis of CuInSe.sub.xS.sub.2-x quantum dots for
sunlight harvesting, J. Phys. Chem. C, 118(30), 16987-16994 (2014),
which is incorporated herein by reference. Briefly, copper(I)
iodide and indium (III) acetate are dissolved in 1-dodecanethiol
(DDT) and oleylamine (OLA) in a round-bottom flask, and the mixture
is degassed under vacuum, with heat, such as from about 50.degree.
C. to about 120.degree. C. The temperature is then raised to
greater than 120.degree. C. such as 140.degree. C. until all solid
precursors are fully dissolved, which usually takes less than 15
min. Separately, a solution of 1 M OLA/DDT-Se is made by mixing Se
powder in OLA and DDT, in a ratio of 1 mmol Se:0.75 mL OLA:0.25 mL
DDT, at room temperature under argon. The flask is then heated to
170-210.degree. C. under argon, whereupon a desired amount of the
OLA/DDT-Se solution is added dropwise such that the temperature of
the reaction mixture does not vary by more than about 3.degree. C.
The temperature is maintained for 10 additional minutes to allow
for QD nucleation (this step can be skipped for injections of
.ltoreq.0.5 mL of OLA/DDT-Se), then the temperature is set to
230.degree. C. for 1-60 min, dependent on the desired size (for
instance, about 10 min for 3.5 nm QDs). The heating element is then
removed and the QDs are allowed to cool. The resulting CISeS QDs
are purified by iterative dissolution in chloroform and
precipitation with methanol and then stored in chloroform, octane,
or 1-octadecene under an inert atmosphere. The reaction is scalable
and typically results in more than a 90% chemical yield of QDs
(relative to Cu and In precursors).
[0082] An alternative exemplary method of making the nanocrystals
comprises mixing a solution of QD cores in a suitable solvent, such
as octadecene (ODE) and oleylamine. A suitable solvent is any
solvent that will dissolve the QD cores. Exemplary solvents
include, but are not limited to, hexane, toluene, chlorinated
solvents such as chloroform and dichloromethane, THF, alcohols such
as methanol, ethanol propanol and isopropanol, cyclohexane or
combinations thereof. The mixture is then degassed. The degassing
may take place at room temperature or at elevated temperatures. In
some embodiments, the degassing is started at room temperature for
a period of time, such as for 30 minutes to greater than 2 hours,
or for 1 hour to 1.5 hours, and then the temperature is raised for
a second period of time, such as from 50.degree. C. to 150.degree.
C. or from 75.degree. C. to 120.degree. C. The degassing may
continue at the elevated temperature for a sufficient period of
time to remove the solvent and any water, such as for from 1 minute
to greater than 30 minutes, or from 5 minutes to 15 minutes. In
certain embodiments, the degassing continues at 100.degree. C. for
5 minutes.
[0083] The solution is then stirred in an inert atmosphere, such as
under nitrogen or argon, and the temperature is raised to above
300.degree. C., such as from greater than 300.degree. C. to
350.degree. C., or from 305.degree. C. to 315.degree. C. In certain
embodiments, the temperature is raised to above 310.degree. C. At
200.degree. C. a solution of metal-oleate in ODE and a separate
solution of octanethiol dissolved in ODE are added slowly, such as
at a rate of 2.5 mL per hour. After 2 hours a portion of oleic acid
is added and after 4 hours a second portion of oleic acid is added.
After 8 hours, the solution is stirred for an additional 15 minutes
at about 310.degree. C., and the heating is removed. The final
product is recovered by precipitation, such as by the addition of
acetone. By varying the amounts of the metal-oleate and octanethiol
and the addition times, QDs of different desired shell-thicknesses
can be produced.
[0084] Another alternative exemplary method can be found in
Pietryga, J. M. et al. Utilizing the Lability of Metal Selenide to
Produce heterostructured Nanocrystals with Bright, Stable Infrared
Emission. J. Am. Chem. Soc. 130, 4879-4885 (2008). Briefly, large,
nearly spherical M.sub.1Se nanocrystals (that is, M.sub.1Se QDs)
with radii from 3.5 to 5 nm were fabricated, and then partial
cation exchange was applied to create an outer M.sub.2Se shell of
controlled thickness by exchanging ions of M.sub.1.sup.2+ with
M.sub.2.sup.2+. Using a moderate reaction temperature (130.degree.
C.) the formation of homogeneous CdSe particles was avoided, and
M.sub.1Se/M.sub.2Se QDs of fairly uniform sizes were produced. This
procedure preserved the overall size of the QDs and allowed the
gradual tuning of the aspect ratio of the resulting core/shell
structure (p), defined as the ratio of the shell thickness (H) to
the total radius (R):.rho.=H/R. Both the starting M.sub.1Se QDs and
the final M.sub.1Se/M.sub.2Se structures exhibited a nearly
spherical shape and fairly narrow size dispersity (standard
deviation of the overall size is approximately 7%). The core and
shell sizes within a given sample appeared less uniform, exhibiting
approximately 15% dispersion.
[0085] B. Polymer
[0086] In some embodiments, the transparent matrix comprises a
polymer that is at least partially, and may be substantially,
transparent to the light, such as visible light, IR light, UV light
or combinations thereof. The transparent matrix may comprise a
polymer suitable for processing into any desired form, such as a
planar substrate or self-standing bulk material, a coating film
such as for a coating on glass of plastic substrates, intercalated
layer such as between two glass or plastic slabs, a fiber such as
an optical fiber made of polymeric materials (plastic optical
fiber) or a viscous fluid suitable for use in transparent
packaging. In some embodiments, the transparent matrix is a polymer
matrix suitable for use in a semi-transparent or substantially
transparent window.
[0087] In some examples, the polymer matrix comprises a polymer
selected from poly acrylate and poly acryl methacrylate,
polyolefin, poly vinyl, epoxy resin (polyepoxide), polycarbonate,
polyacetate, polyamide, polyurethane, polyketone, polyester,
polycyanoacrylate, silicone, polyglycol, polyimide, fluorinated
polymer, polycellulose, or poly oxazine. Exemplary polymers
include, but are not limited to, polyethylene, polypropylene,
polymethylpentene, polybutebe-1, polyisobutylene, ethylene
propylene rubber, ethylene propylene diene monomer rubber,
polyvinyl chloride, polybutadiene, polystyrene, polyvinyl acetate,
polyvinyl alcohol, polyacrylonitrile, bisphenol-A, bisphenol-F,
polytetrafluoroethylene, polyvinylfluoride, polyvinylidene
fluoride, polychlorotrifluoroethylene, ethylene-carbon monoxide
co-polymer, polyglycolide, polylactic acid, polycaprolactone,
polyhydroxyalkanoate, polyhydroxybutyrate, polyethylene adipate,
polybutylene succinate, polyethylene glycol, methyl cellulose,
hydroxyl methyl cellulose, polymethyl methacrylate, polymethyl
acrylate, polyethyl acrylate, polylauryl methacrylate or
combinations thereof.
[0088] In some embodiments, the polymer matrix comprises an
acrylate polymer, and may be an alkyl acrylate polymer. The
acrylate polymer may also be a substituted acrylate polymer, where
one or more of the vinyl hydrogens in the monomer is replaced by
one or more substituent groups. In some embodiments, the
substituent group is an alkyl group, such as methyl, ethyl, propyl,
isopropyl, or butyl. Exemplary acrylate monomers that can be used
to form the polymers include, but are not limited to, methyl
acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, hexyl
acrylate, heptyl acrylate, octyl acrylate, nonyl acrylate, decyl
acrylate, undecyl acrylate, lauryl acrylate, dodecyl acrylate,
stearyl acrylate, 2-chloroethyl acrylate, methyl methacrylate
(MMA), ethyl methacrylate, butyl methacrylate, lauryl methacrylate,
2-ethylhexyl acrylate, hydroxyethyl methacrylate, or
trimethylolpropane triacrylate (TMPTA). The acrylate or
methacrylate monomer may be selected to provide long side chains,
such as C6-C25 side chains, C8-C25 side chains or C10-C25 side
chains. In some embodiments, the side chain group on the monomer is
hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, lauryl,
tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl,
nonadecyl, eicosyl, or a combination thereof. In particular
embodiments, the polymer matrix is polylauryl methacrylate (PMMA),
which provides side chains having a length of C12.
[0089] The polymer matrix may also comprise one or more
cross-linking agents. A person of ordinary skill in the art will
understand that the type of cross-linking agent may depend on the
type of polymer being used. For example, a diacrylate cross-linking
agent may be sued to cross link a polyacrylate polymer matrix. In
some embodiments, the cross-linking agent is a diacrylate or
dimethacrylate. The cross-linking agent may be an alkyl or alkyl
oxide diacrylate or dimethacryalte, and in particular embodiments,
the cross-linking agent is ethylene glycol dimethacrylate.
[0090] The nanocrystals may be dispersed in the polymer matrix. In
some embodiments, the QDs are dispersed in the polymer matrix by a
process that inhibits or substantially prevents aggregation of the
nanocrystals. The dispersion may be such that an emission
efficiency of the nanocrystals in the polymer matrix is
substantially the same as the emission efficiency of the
nanocrystals in a solution, such as a hexane solution. In some
embodiments, the emission efficiency of the nanocrystals in the
polymer matrix is at least 90% of the emission efficiency of the
nanocrystals in a hexane solution, such as at least 95%, at least
98% or at least 99%.
[0091] In some embodiments, the nanocrystals are dispersed such
that the average distance between the nanocrystals is greater than
an energy transfer distance. Energy transfer between nanocrystals
typically occurs at distances up to about 15-20 nm. Therefore, in
certain embodiments, the average distance between the nanocrystals
is greater than 15 nm, such as greater than 20 nm, greater than 25
nm or greater than 30 nm. In some embodiments, the concentration of
nanocrystals in the polymer matrix is from greater than 0 to 10%
relative to the weight of the polymer matrix, such as from greater
than 0 to 5%, from greater than zero to 1% or from greater than
zero to 0.5%. In certain embodiments, the concentration of
nanocrystals in the polymer matrix is from 0.1% to 0.2%.
[0092] The composition may be a substantially colorless
composition. In some embodiments, the composition has a color
rendering index of greater than 80, such as from 80 to 100, from 85
to 100 or from 90 to 100. In other embodiments, the composition has
a total error score from a Farnsworth-Munsell 100 hue color vision
test of less than 100, such as from 0 to 90, from 0 to 80 or from 0
to 70, indicating an insignificant amount of color distortion being
experienced by test subjects.
[0093] The composition may absorb at least 10%, or at least 20%, of
the incident solar power. In some embodiments, the composition has
an optical power conversion efficiency of greater than 1%, such as
greater than 2%, or greater than 3%.
[0094] C. Sol-Gel
[0095] In some embodiments, the nanocrystals are mixed with a lower
alcohol, a non-polar solvent and a sol-gel precursor material, and
the resultant solution can be used to form a solid composition. For
example, the solution can be deposited onto a suitable substrate to
yield substantially homogeneous, solid compositions from the
solution of nanocrystals and sol-gel precursor. "Homogeneous" means
that the nanocrystals are substantially uniformly dispersed in the
resultant product. In some instances, non-uniform dispersal of the
nanocrystals is acceptable. In some embodiments of the invention,
the solid compositions can be transparent or optically clear.
[0096] The lower alcohol used in this process is generally an
alcohol containing from one to four carbon atoms, i.e., a C.sub.1
to C.sub.4 alcohol. Among the suitable alcohols are included
methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol
and t-butanol.
[0097] The non-polar solvent is used in the process to solubilize
the nanocrystals and should be miscible with the lower alcohol. The
non-polar solvent is generally chosen from among tetrahydrofuran,
toluene, xylene and the like. Tetrahydrofuran is a preferred
non-polar solvent in this process.
[0098] Sol-gel processes generally refer to the preparation of a
ceramic material by preparation of a sol, gelation of the sol and
removal of the solvent. Sol-gel processes are advantageous because
they are relatively low-cost procedures and are capable of coating
long lengths or irregularly shaped substrates. In forming the
sol-gel based solution used in the processes of the present
invention, suitable sol-gel precursor materials are mixed with the
other components.
[0099] Additional information regarding Sol-gel processes can be
found in Brinker et al., "Sol-Gel Science, The Physics and
Chemistry of Sol-Gel Processing", Academic Press, 1990, which is
incorporated herein by reference. Among suitable sol-gel precursor
materials are included metal alkoxide compounds, metal halide
compounds, metal hydroxide compounds, combinations thereof and the
like where the metal is a cation from the group of silicon,
titanium, zirconium, and aluminum. Other metal cations such as
vanadium, iron, chromium, tin, tantalum and cerium may be used as
well. Sol solutions can be spin-cast, dip-coated, printed or
sprayed onto substrates in air. Sol solutions can also be cast into
desired shapes by filling molds or cavities as well. Among the
suitable metal alkoxide compounds can be included titanium
tetrabutoxide (titanium (IV) butoxide), titanium tetraethoxide,
titanium tetraisopropoxide, zirconium tetraisopropoxide,
tetraethoxysilane (TEOS). Among suitable halide compounds can be
included titanium tetrachloride, silicon tetrachloride, aluminum
trichloride and the like.
[0100] The sol-gel based solutions generated in this process are
highly processable. They can be used to form solid compositions in
the shape of planar films and can be used to mold solid
compositions of various other shapes and configurations. Volume
fractions or loadings of the nanocrystals can been prepared as high
as about 13 percent by volume and may be as high as up to about 30
percent by volume. Further, the first process of the present
invention has allowed preparation of solid compositions with a
refractive index of 1.9, such refractive index values being
tunable.
[0101] In alternative embodiments, the process for incorporating
nanocrystals into a sol-gel host matrix further comprises admixing
the nanocrystals with a polymer. Typically this is done in a
suitable solvent, such as a solvent that will dissolve the polymer.
A person of ordinary skill in the art will understand that the
nature of the solvent will depend on the polymer which needs to be
dissolved. Suitable solvents include, but are not limited to,
chlorinated solvents such as chloroform, dichloromethane,
dichloroethane and tetrachloroethane. The polymer solution is then
added to a solution of nanocrystals in a suitable solvent, such as
chloroform. In some embodiments, the nanocrystals have been
previously separated from their growth media, such as by
precipitation. When sufficient polymer has been added such that the
nanocrystals are soluble in an alcohol, such as ethanol, the
solvent is evaporated. The nanocrystal/polymer mixture is dissolved
in alcohol, typically in an inert atmosphere. In some instances
where minor amounts of nanocrystal-polymer adduct or complex
remained un-dissolved in the alcohol, a co-solvent such as
tetrahydrofuran and the like is used with the alcohol to completely
or nearly completely solubilize the adduct or complex. The solution
is then mixed with a sol-gel precursor solution, e.g., a titania
sol precursor material, and formed into a solid composite such as a
film on a substrate. Once incorporated into the sol-gel matrix, the
nanocrystals are highly stable and are not then soluble within
hydrocarbon solvents such as hexane. The alcohols, used with the
alcohol soluble colloidal nanocrystal-polymer adduct or complexes
in the present invention, generally include ethanol, 1-propanol and
1-butanol. Other alcohols may be used as well, but alcohols having
lower boiling points are preferred for improved processability with
sol-gel precursors.
[0102] Additional information regarding the process of preparing a
composition comprising quantum dots dispersed within a sol-gel host
matrix can be found in U.S. Pat. Nos. 7,226,953, 7,723,394 and
8,198,336, which are incorporated herein by reference.
[0103] D. Solvent Matrices
[0104] In alternative embodiments, the nanocrystals are dispersed
in a solvent matrix. The solvent can be any solvent suitable for
solubilizing the nanocrystals. Suitable solvents include non-polar
solvents, such as tetrahydrofuran, toluene, xylene and the like.
The solvent may be a single solvent, or it may be a mixture of
solvents. A composition comprising a solvent matrix may be used
when the composition will be loaded into a space between two
layers, typically transparent layers. Examples include, but are not
limited to, loading the composition into the space between two
panes of glass, such as two window panes.
IV. Method of Making the Composition
[0105] Also disclosed herein are embodiments of a method for making
the composition. In some embodiments, the method comprises mixing
the nanocrystals with a small volume of a monomer, and then mixing
the resulting mixture with a larger volume of the monomer. One or
more cross-linking agents and/or initiators may also be added. In
some embodiments, the nanocrystals are mixed with the small volume
of monomer for a time sufficient to wet the surfaces of the
nanocrystals and/or allow for a fine dispersion of nanocrystals in
the monomer to develop. Suitable cross-linking agents include any
agent that can cross-link the polymer being made. A person of
ordinary skill in the art will understand that the exact nature and
amount of the cross-linking agent may depend on the monomer being
used. In certain embodiments, an acrylate cross-linker is used,
such as ethylene glycol dimethacrylate. The amount of cross-linking
agent is selected to provide a desired amount of cross-linking in
the resultant polymer. In some embodiments, the ratio of monomer to
cross-linking agent is from less than 50%:50% wt/wt to greater than
99%:1% wt/wt, such as from 60%:40% wt/wt to 99%:1% wt/wt, from
75%:25% wt/wt to 95%:5% wt/wt or from 70%:30% wt/wt to 90%:10%
wt/wt. In certain embodiments, the ratio of monomer to
cross-linking agent is 80%:20% wt/wt.
[0106] An initiator may be used to facilitate polymerization of the
monomer. The initiator can be any initiator suitable for the
particular monomer being used. In some embodiments, the initiator
is a radical photoinitiator. Suitable initiators include, but are
not limited to, peroxides such as lauroyl peroxide, di-tert-butyl
peroxide, benzoyl peroxide, methyl ethyl ketone peroxide,
tert-butyl peracetate, tert-butyl hydroperoxide and acetone
peroxide, azo compounds such as azobisisobutyronitrile (AIBN),
1,1'-azobis(cyclohexanecarbonitrile) (ABCN) and
4,4'-azobis(4-cyanovaleric acid) (ABVA), photoinitiators such as
2,2-dimethoxy-1,2-diphenylethan-1-one (IRGACURE.RTM. 651),
persulfates such as potassium persulfate, sodium persulfate and
ammonium persulfate, organometallics such as triethylaluminum and
titanium tetrachloride, or combinations thereof. Sufficient
initiator is added to the monomer to initiate the polymerization
reaction. In some embodiments, the amount of initiator added to the
monomer or monomers is from greater than 0 to greater than 5% wt/wt
with respect to the monomer(s), such as from greater than 0 to 5%
wt/wt, from 0.1% to 2.5% wt/wt, or from 0.5% to 1.5% wt/wt. In
certain embodiments, 1% wt/wt initiator is added to the
monomer(s).
[0107] After the nanocrystal/monomer mixture has been mixed with
the larger volume of monomer, and any desired cross-linking agents
and/or initiators added, the mixture is agitated to facilitate
nanocrystal dispersion. Any suitable agitation can be used, such as
stirring, sonication, shaking or any combination thereof. The
agitation is continued until a suitable dispersion is formed. The
mixture is then typically poured into a mold and polymerization is
initiated. The polymerization can be initiated by any suitable
technique, such as heating or irradiation, and may proceed in a
light or a dark environment, and at an ambient temperature or an
elevated or reduced temperature relative to the ambient
temperature. A person of ordinary skill in the art will appreciate
that the method of initiation may depend on the type of initiator
used. In certain embodiments, the initiation was achieved by
irradiation, such as UV irradiation. After polymerization is
complete, the composition can be removed from the molds, shaped or
cut in to a desired shape, and polished.
V. Applications
[0108] The disclosed compositions can be used in a variety of
applications and devices such as solar cells and other applications
comprising photovoltaic cells. One exemplary embodiment of a device
is schematically shown in FIG. 4. With reference to FIG. 4, device
100 comprises an LSC 110 comprising a composition as disclosed
herein, comprising a transparent matrix and nanocrystals. The
device 100 also comprises photovoltaic cells, with the exemplary
illustrated embodiment comprising four photovoltaic cells 120, 130,
140 and 150. The composition receives incident light, such as from
the sun, and some of that light is absorbed by the nanocrystals.
The photovoltaic cells receive the luminescence emissions from the
nanocrystals.
[0109] In alternative embodiments, one, two or three of the
photovoltaic cells, 120, 130, 140 and 150 may be replaced with
reflectors and/or diffusers, such as white or silvered reflectors,
reflectors coated with aluminum or other metals, or multilayer
stacks of dielectric layers to form distributed Bragg reflectors.
The function of the reflector is to reflect light back into the
composition and towards the photovoltaic cell(s). In some
embodiments, the reflectors are diffuse reflectors.
[0110] In other examples, the LSC 110 may not be surrounded by
photovoltaic cells and/or reflectors. In these examples, any edge
that does not have a reflector or photovoltaic cell may allow light
to escape, thereby reducing the overall efficiency of the
device.
[0111] In some embodiments, the LSC 110 is transparent or
semi-transparent, allowing the device to be used as a window. In
such embodiments, the photovoltaic cells and reflectors and/or
diffusers, if present, may be placed in the window frame. The
window may be of any suitable shape, such as a square or rectangle,
circle, ellipse, triangle, pentagon, hexagon, octagon, arch, cross,
star or an irregular shape. The window may be colored or colorless,
tinted or not tinted, and in all possible combinations. In some
embodiments, the window is two way, that is visible light can pass
in both directions through the window pane. In other embodiments,
the window is a `one-way` window, thereby restricting the passage
of visible light through the window. Ultraviolet and infrared light
mat still be able to penetrate the window. In other embodiments,
the window can be transparent in the visible and IR but strongly
absorb UV light. In some embodiments, the window is in a building
or in a transportation device, such as an automobile, ship or
airplane.
VI. Examples
Materials
[0112] Lauryl methacrylate (LMA, 99%, Aldrich) and ethylene glycol
dimethacrylate (EGDM, 98%, Aldrich), purified with basic activated
alumina (Sigma-Aldrich), were used as monomers for the preparation
of polymeric nanocomposites. IRGACURE.RTM. 651 (Sigma-Aldrich) was
used as a photo-initiator without purification.
Synthesis of the QDs
[0113] The CIS and CISeS QDs used in this study were synthesized
following the procedure described in McDaniel, H., Koposov, A. Y.,
Draguta, S., Makarov, N. S., Pietryga, J. M. & Klimov, V. I.,
Simple yet Versatile Synthesis of CuInSe.sub.xS.sub.2-x Quantum
Dots for Sunlight Harvesting. J. Phys. Chem. C 118, 16987-16994
(2014), which is incorporated herein by reference. Typically,
copper (I) iodide and indium (III) acetate were dissolved in a
mixture of 1-dodecanethiol (DDT) and oleylamine (OLA) in a round
bottom flask, and the mixture was degassed for 30 minutes. For
CISeS, a solution of 1 M OLA/DDT-Se was made separately by mixing
selenium powder in OLA and DDT. The reaction flask was then heated
to 230.degree. C. for about 30 minutes, with OLA/DDT-Se added
during heating for CISeS (otherwise, reaction was approximately the
same for CIS). The resulting CISeS QDs were purified by iterative
dissolution in chloroform and precipitation with methanol, and then
stored in chloroform. For improved PL QY and stability, the QDs
were exposed to a solution of zinc oleate at elevated temperature
that formed a thin ZnS shell by cation exchange as described in
McDaniel, H., Fuke, N., Makarov, N. S., Pietryga, J. M. &
Klimov, V. I. An integrated approach to realizing high-performance
liquid-junction quantum dot sensitized solar cells. Nat. Commun. 4
(2013), which is incorporated herein by reference.
Fabrication of the Nanocrystal-Polymer Composite
[0114] Initially, a QD powder was dispersed in a small volume of
lauryl methacrylate monomer for 3 hours in order to wet the
nanoparticle surface and enable a fine dispersion of the individual
QDs to form. The monomer-QD mixture was then added to a large
volume of lauryl methacrylate together with a secondary monomer,
ethylene glycol dimethacrylate (EGDM; LMA:EGDM 80%:20% w/w), which
acted as a cross-linking agent, and a radical photo-initiator
(IRGACURE.RTM. 651; 1% w/w). After stirring the mixture for 20
minutes and sonication for 10 minutes to facilitate QDs dispersion,
the homogeneous mixture was poured into a mold made of two
low-roughness pieces of tempered glass linked by a PVC gasket, and
irradiated with 365 nm light from a UV lamp for 5 minutes in order
to trigger radical polymerization. The polymerization was then
completed by keeping samples in dark for 30 minutes while leaving
them in the mold in order to avoid creation of cracks. After the
completion of the procedure, the slabs were removed from the mold,
cut in pieces of desired sizes, and polished.
Application of a Nanocrystal-Polymer Composite Coating
[0115] The nanocrystal-polymer composites described above, or
others, may be applied as a coating on top of a waveguiding
material such as glass. The emission from the QDs couples into the
glass due to the same or similar index of refraction of the coating
and the glass. The glass may be more robust than the polymer itself
and also have flatter surfaces, conduced for total internal
reflection. Furthermore, the glass may have even greater
transparency than the polymer such that it acts as a better light
guide. Deployment of the coating embodiment may also be lower cost
because it can be accomplished by spray deposition, dip coating, or
other high throughput deposition approaches. The coating can be
nanocrystals within many different types of initially liquid
solutions including paint, polymer, nail polish, epoxy resin,
silicone, sol-gels, or others.
Characterization of the Polymeric Nanocomposite
[0116] Differential scanning calorimetry measurements were
performed by using a Mettler Toledo Star.RTM. thermal analysis
system. The thermal program was characterized by three ramps: the
first step of heating from 0.degree. C. to 200.degree. C. at
10.degree. C. per minute, followed by the step of cooling from
200.degree. C. to 0.degree. C. at -10.degree. C. per minute, and
the final step of heating from 0.degree. C. to 200.degree. C. at
10.degree. C. per minute.
[0117] FIG. 5 provides Differential Scanning calorimetry curves of
the pure polymer (LSC0) and CISeS QDs/P(LMA-co-EGDM) nanocomposites
(LSC10 and LSC20). First and second heating scans showed a
transition glass temperature (T.sub.g) of -65.degree. C., in good
agreement with literature. Moreover, the absence of exothermic
phenomena (upwards peaks) during the first heating ramp indicated
that the polymerization process had proceeded to completion.
[0118] During thermogravimetry (TGA) measurements carried out using
a TA Q500 analyzer (TA Instruments) samples were heated to
800.degree. C. at 10.degree. C./minute in air. FIG. 6 provides TGA
(Thermo-gravimetric) and DTA (differential thermo-gravimetric)
curves of the pure polymer (LSC0) and CISeS QDs/P(LMA-co-EGDM)
nanocomposites (LSC10 and LSC20). The weight of the residual
corresponds to the amount of the QDs in the polymeric matrices: 0.3
wt % in LSC10 and 0.5 wt % in LSC20.
Spectroscopic Studies
[0119] All spectroscopic studies were carried out using toluene
solutions of QDs loaded into quartz cuvettes and QD-PLMA
nanocomposites. In the measurements of PL dynamics, the samples
were vigorously stirred to avoid the effects of photocharging.
Absorption spectra of QD solutions and QD-polymer composites were
measured with a Perkin Elmer LAMBDA 950 UV/Vis/NIR
spectrophotometer. PL, PLE and spectra and transient PL
measurements were carried out using excitation with <70 ps
pulses at 3.1 eV from a pulsed diode laser (Edinburgh Inst. EPL
series). The emitted light was collected with a
liquid-nitrogen-cooled low-noise Hamamatsu NIR (R5509-73)
photomultiplier tube (PMT) coupled to time-correlated single-photon
counting (TCSPC) electronics (time resolution about 150 ps).
Optical measurements on LSCs were carried out by coupling the
output edge of the slab to an integrating sphere and using a 532 nm
cw laser as an excitation source. The PL was detected with the same
PMT and the TCSPC unit describe earlier. The same setup was used
for PL quantum yield measurements.
[0120] Transient absorption measurements were performed using a
LabView-controlled home-build setup in a standard pump-probe
configuration with 400-nm, approximately 100-fs pump pulses (1 kHz
repetition rate) and a broad-band, white light supercontinuum
probe. The excitation spot diameter was 800 .mu.m at the 1/e.sup.2
level. The measurements were performed on QD solutions with optical
density (OD) below 2 at 400 nm, which corresponded to QD
concentrations of less than 1.times.10.sup.-5 M. All the
measurements were conducted under oxygen-free and moisture-free
conditions using air-tight quartz cuvettes. The organic solvents
used were dry and stored under argon. Sample preparation was done
at inert atmosphere in a glovebox.
Monte Carlo Ray Tracing Simulation
[0121] The theoretical analysis of the efficiency of the LSC was
performed via a Monte Carlo ray tracing method in which propagation
of a photon within the LSC was modeled as propagation of a
geometrical ray subject to refraction/reflection at the air-LSC
interfaces according to Fresnel Laws. Accordingly, no interference
was taken into account. The stochastic nature of the simulations
was reflected in the fact that the ray was not split upon reaching
an interface but rather either transmitted or reflected with the
probabilities proportional to respective energy fluxes given by
Fresnel Laws. The dependence of these probabilities on the state of
polarization of the incident ray (e.g., s- or p-polarized) was also
taken into account. A specific event (i.e., transmission or
reflection) was chosen according to random Monte Carlo drawing.
[0122] Inside the LSC material, for each ray, the inverse transform
sampling method was applied to randomly generate the length of the
optical path before absorption by QDs. Path lengths follow the
exponential attenuation law determined by the wavelength-dependent
absorption cross-section, .sigma.(.lamda.), and the QD
concentration, N.sub.QD, via an attenuation coefficient,
k(.lamda.)=N.sub.QD.sigma.(.lamda.). Since the mean path length,
given by the inverse attenuation coefficient is always much greater
than the average distance between QDs, there was no need to keep
track of an explicit position of each QD, so the LSC material
(PMMA+QDs) was considered within the effective medium approach,
i.e., as a uniform material with the attenuation coefficient
defined above.
[0123] Once a photon was absorbed by a QD, the subsequent fate of
the excitation (i.e., reemission or non-radiative relaxation) was
again determined by the Monte Carlo sampling according to the PL
quantum yield. The direction of reemission was distributed
uniformly and the reemission wavelength was determined using the
rejection sampling applied to the accurate QD PL spectrum obtained
from experiment.
[0124] The ultimate fate of each photon was either loss due to
non-radiative recombination or escape from the LSC via one of the
interfaces. A single-ray Monte Carlo simulation was typically
repeated 10.sup.5-10.sup.7 times to have a proper statistical
averaging.
Colorimetry Studies
[0125] CIE-L*a*b* color coordinates were extracted from the
reflectance spectra measured with a Perkin Elmer Lambda 9000
spectrometer using to an integrating sphere and placing a
Spectralon.RTM. scatterer on the back side of the LSCs, following
the conventional procedure for colorimetric measurements on
semitransparent materials. Both diffused and reflected light
(8.degree.) were collected. D65 illuminant spectrum was used for
the calculation of the L*, a*, b* coordinates.
[0126] Color rendering index of the light transmitted by the LSCs
was calculated following CIE13.3 procedure using eight Munsell test
color samples (TCS). A D65 illuminant spectrum was employed both as
a reference light source and as a light source filtered by the
experimental absorption spectra of the LSCs.
[0127] Farnsworth-Munsell 100 hue color vision tests were performed
on 40 non-color blind subjects between 20 and 55 years of age. In
order to account for individual differences in color sensitivity
across the whole statistic population, for each subject the test
was performed in identical conditions both without any filter, and
by filtering the subject's vision using the LSCs. The chronologic
order of tests in the three conditions was chosen randomly across
the population to avoid results to be biased by learning effects.
The test was conducted on a calibrated monitor (Dell Vostro
3750).
Results and Discussion
[0128] CISeS QDs coated with ZnS were used to realize large-area IR
QD-LSCs with reduced re-absorption losses and extended coverage of
the solar spectrum. Specifically, CISeS QDs that had an emission at
960 nm (1.3 eV) were used, which was near optimal for LSCs coupled
to Si PVs, and also allowed for the realization of colorless
QD-doped slabs that are similar to neutral density filters and
therefore well suited for applications as semitransparent windows.
Overcoating CISeS QDs with a shell of a wide-gap ZnS allowed the
spectral properties of emission to be preserved, as well as the
emission efficiency upon exposure of the QDs to the radical
polymerization initiators. By incorporating QDs into a
photopolymerized, cross-linked polylauryl methacrylate (PLMA)
matrix, freestanding, colorless polymer slabs of excellent optical
quality were obtained that introduced no chromatic distortion. The
lack of chromatic distortion was demonstrated by both color
rendering index (CRI) measurements and a comparative
Farnsworth-Munsell 100 hue discrimination test. Using this
approach, and without the assistance of any back reflector, an
optical power conversion efficiency .eta.=P.sub.OUT/P.sub.IN=3.2%
was achieved, where P.sub.OUT is the luminous power collected by
the photodiodes coupled to the LSC perimetral edges, and P.sub.IN
is the solar power incident onto the LSC surface. Finally, PL and
transient absorption (TA) studies of the I-III-VI.sub.2 QDs were
conducted to elucidate the light emission mechanism and the nature
of a large Stokes shift. These measurements suggested that light
emission occurred via a transition involving a conduction band
electron and a hole residing in a deep intra-gap state, which was
likely associated with a "native" defect such as Cu.sup.2+.
[0129] FIG. 7 shows the optical absorption and PL spectra of
representative ZnS-coated CISeS QDs dissolved in toluene (red and
black lines, respectively) where they are compared to the
terrestrial spectrum of solar radiation (grey shading) and a
typical EQE spectrum of a Si PV (green line). The absorption
spectrum showed almost a featureless profile characteristic of
ternary QDs and extended over the entire range of visible
wavelengths, which allowed for efficient capture of solar
radiation. The PL spectrum closely matched the low-energy part of
the EQE spectrum of a crystalline silicon PV cell, which
corresponded to a near-optimal situation for converting re-emitted
photons into electrical current. The reported EQE curve was the
efficiency response of the 1 cm.times.2.5 cm c-Si PV cells used to
build the concentrators (see below), which were not optimised for
maximum power conversion efficiency. Using high performance PV
cells with optimized design, or top-notch commercial modules, such
as Sunpower X series, will allow for further extending the solar
coverage and for boosting the efficiency of QD-LSCs without
introducing extra fabrication costs.
[0130] The absorption spectrum exhibited a weak shoulder at
approximately 640 nm (1.85 eV), which marked the position of the QD
band edge. It was displaced from the PL band by 550 meV, which
indicated a very large Stokes shift (As), greatly exceeding that of
standard "core-only" CdSe, PbS or PbSe QDs where it is typically a
few tens of meV. An exceptionally large value of As is a general
property of I-III-VI.sub.2 QDs and is characteristic of both pure
(CIS and CISe) and alloyed compositions.
[0131] To retain a high emission efficiency of the QDs during the
encapsulation procedure, the emitting CISeS cores were protected
with a shell of wide gap ZnS by adopting approach from McDaniel,
H., Fuke, N., Pietryga, J. M. & Klimov, V. I., Engineered
CuInSe.sub.xS.sub.2-x Quantum Dots for Sensitized Solar Cells. J.
Chem. Phys. Lett. 4, 355-361 (2013), which is incorporated herein
by reference. As a matrix material, a cross-linked PLMA was used,
which belongs to the family of acrylate polymers. Its long
side-chains prevented agglomeration of the QDs and allowed for
fabrication of high optical quality QD-polymer nanocomposites.
Further, PLMA has a glass transition temperature of -65.degree. C.,
and at room temperature represented a rubber-like material with
long alkyl side chains that display dynamics resembling those of
liquids. Since the polar methacrylate main chain and the nonpolar
alkyl side chains are immiscible, the polymer bulk is phase
separated at the nanoscopic level, which provided the QDs with
local environment which was very similar to that of 1-octadecene or
analogous solvents used in the QD synthesis. This specially
designed near-native polymeric environment may help maintain
long-term stability of the QDs.
[0132] The chemical structures of the organic precursors employed
in the fabrication of the slabs are shown below.
##STR00001##
[0133] The fabrication procedure consisted of initially wetting the
QDs in a small volume of lauryl methacrylate monomer for 3 hours to
enable a fine dispersion of the individual particles to form. The
monomer-QD mixture was then added to a large volume of monomer
together with radical photo-initiator (IRGACURE 651; 1% w/w) and
ethylene glycol dimethacrylate (EGDM; LMA:EGDM 80%:20% w/w) that
acted as a cross-linking agent. It was important that the EGDM
molecules, which bridge the main chains and help the mechanical
stability of the slabs, were located in the hydrophobic domains of
the nanocomposite and thus were spatially separated from the QDs
and therefore unlikely to alter their electronic properties. After
stirring the mixture for 20 minutes and sonication for 10 minutes,
the LSCs were fabricated following a cell-casting procedure
typically used for the preparation of optical grade polymer slabs
(FIGS. 8A and 8B). Briefly, the homogeneous mixture was poured into
a mold of low roughness tempered glass and irradiated with 365 nm
light for 5 minutes in order to trigger radical polymerization. The
polymerization was then completed by keeping samples in dark for 30
minutes while leaving them in the mold in order to avoid creation
of cracks. After the completion of the procedure, the slabs were
removed from the mold, cut in pieces of desired sizes, and
polished. A high optical quality of the fabricated composites is
illustrated by a photograph in FIG. 8B which shows an LSC based on
CISeS QDs and P(LMA-co-EGDM) with dimensions of 12 cm.times.12
cm.times.0.3 cm.
[0134] Spectroscopic studies of the fabricated composites
demonstrated that the spectral and dynamical properties of
ZnS-coated CISeS QDs were unaffected by the radical polymerization
procedure. Specifically, both the absorption and PL spectra of the
QDs in the polymer matrix were essentially identical to those of
the QDs in toluene solution (FIG. 9) and so is the PL quantum yield
(.PHI..sub.PL=40.+-.4%) measured using an integrating sphere under
continuous wave (cw) excitation at 473 nm. FIG. 9 also provides the
absorption spectrum of the P(LMA-co-EGDM) matrix. The absence of
additional nonradiative decay channels in the nanocomposites was
confirmed by the analysis of the PL dynamics (FIG. 10). In FIG. 10,
the top trace is from ZnS-coated CISeS QDs in toluene; the second
trace from the top is from QDs in lauryl methacrylate; and traces
three through six from the top are QDs in an LMA-co-EGDM matrix,
with different traces corresponding to different times after
completion of the polymerization. FIG. 10 illustrates that the PL
decay measured for the ZnS-coated QDs in toluene was essentially
identical to that of the QDs in the LMA:EGDM:IRGACURE.RTM. mixture
both before and after activation of the radical photocatalyst. In
contrast, uncoated CISeS QDs underwent about 50% PL quenching upon
activation of the radical catalyst (FIG. 11). This highlights the
important role played by a wide-gap ZnS passivation in preserving
light-emitting properties of the QDs core in the case of various
chemical treatments.
[0135] After characterizing light emitting properties of the
fabricated nanocomposites, the optical losses due to re-absorption
were analyzed. To illustrate how the QD PL excited across the
waveguide was guided towards the slab edges, FIG. 12 shows a
photograph of an exemplary devices under UV illumination taken with
an UV-filtered IR camera.
[0136] FIG. 13 shows the absorption spectrum of the QD-polymer slab
measured for light incident at a normal angle onto its largest
side. FIG. 13 also displays spectra of photoluminescence collected
at one of the slab edges (12 cm.times.0.3 cm) with an integrating
sphere using cw 532 nm excitation, with the pump spot positioned at
different distances (d from 0 cm to 12 cm) from the sample edge.
The photoluminescence intensity dropped with increasing d (see also
FIG. 14) due to a combined effect of light escape from the
waveguide and re-absorption by the QDs. The shape of the normalized
PL spectra showed only a small change with d (FIG. 13, inset)
suggesting that losses to re-absorption are not significant.
Non-normalized PL spectra (main panel) indicated that the overall
PL intensity dropped with increasing d due to scattering at optical
imperfections within the P(LMA-co-EGDM) matrix and photon escape
from the waveguide. FIG. 14 shows the photoluminescence output as a
function of d (white circles; derived by integrating the spectra in
the main panel of FIG. 13) in comparison to the probability of
photon reaching the LSC edge computed using Monte Carlo ray tracing
(shaded in pink for .PHI..sub.PL=40%; and in green for
.PHI..sub.PL=100%). PL output obtained by integrating the
normalized PL spectra in the inset of FIG. 13 is reported as black
triangles.
[0137] In order to distinguish between different mechanisms for
optical losses Monte Carlo ray tracing simulations were performed
using experimental parameters of LSCs fabricated in this work
(FIGS. 15 and 16) and neglecting scattering at optical
imperfections within the slab or at its surfaces. Possible
trajectories of photons generated inside the slab (generation
points are indicated by white dots) are depicted in FIG. 15. The
initial emission of a photon within the LSC, depicted by white
spheres (1), is followed by a photon propagation within the slab
subject to absorption/reemission events (2), shown by purple cubes.
The following ultimate fates of a photon within the LSC are
considered: (3) the photon reaches the LSC edge and is harvested by
the PV cell (red arrows); (4) the photon is lost via absorption by
a QD followed by a nonradiative decay (black balls); and (5) the
photon is lost by escaping through one of the LSC faces not coupled
to a PV (red lines sticking outside the LSC). The probabilities of
these three scenarios was evaluated as a function of the lateral
position of the point of origin of the emitted photon within the
slab considering uniform illumination of the LSC from the top (FIG.
16). In these calculations, experimental absorption and emission
profiles of the QDs embedded into the polymer waveguide were used
(FIG. 9) and (tom was assumed to be 40%. By averaging over
10.sup.5-10.sup.7 different emission events randomly generated
across the device, the total output probability per originally
emitted, first-generation photon was estimated to be 44%, while the
probabilities of a photon loss due to nonradiative decay following
one or more re-absorption events or escape from the waveguide were
respectively 27% and 29%. To highlight the potential of the
disclosed LSCs for the realization of large-area devices applicable
as PV windows, calculations of the output probability as a function
of LSC area for devices up to 2 m.times.2 m were performed, in
comparison to losses due to photon escape from the waveguide and
reabsorption followed by non-radiative decay (FIG. 17). The
simulation indicated that for .PHI..sub.PL=40%, the output
probability dropped to about 50% for a 50 cm propagation length,
whilst for QDs with .PHI..sub.PL=100% the propagation length
required for the 50% optical loss increased up to 1 meter. The
calculations were performed using the experimental absorption
spectrum of the final polymer slab doped with QDs and therefore the
emission losses account also for absorption by the polymer
matrix.
[0138] To evaluate the role of losses due to scattering at optical
imperfections within the fabricated polymer-QD slabs, results of
experiments where PL was excited at different distances from the
LSC edge were modeled (FIG. 13). The simulated evolution of the PL
intensity with d assuming the PL quantum yield of 40% is shown in
FIG. 14 (pink shading) and correlated well with the experimental
data. A fairly close correspondence between the modeling and the
experimental data (white circles) suggested that scattering losses,
disregarded by the model were indeed negligibly small in the
disclosed devices, which again attests to the high optical quality
of the QD-polymer nanocomposites.
[0139] To estimate the ultimate optical power conversion efficiency
achievable with these LSCs, the situation where the QD PL yield
reached the ideal value of 100% (green area in FIG. 14) was
modeled. In this case, the probability to harvest a photon at the
LSC edge increased to 61% while the remaining 39% accounted for
optical losses due to photon escape from the waveguide.
[0140] Further, to distinguish losses due to re-absorption from
those due to photon escape, the normalized PL spectra shown in the
inset of FIG. 13 was analyzed. Specifically, the plot was
spectrally integrated and the results plotted as a function d (FIG.
14, black triangles). In this case, the change in the PL signal can
only occur as a result of spectral distortion caused by light
re-absorption by the QDs. Therefore, these data were used to
quantify emission losses due exclusively to re-absorption. Based on
the plot in FIG. 14, the loss was estimated to be about 30% on a
distance of 12 cm. This value was considerably smaller than
attenuation observed, e.g., for standard, heavy metal-containing
CdSe or PbS QDs, which may be a consequence of the large Stokes
shift characteristic of CISeS QDs. For comparison, standard PbS QDs
with a Stokes shift of about 120 nm show more than 70% losses to
re-absorption on the length of less than 8 cm.
[0141] To quantify the efficiency of the fabricated LSCs, a
characterization setup shown in FIG. 18 was used, to study two
samples that absorb 10% (LSC10, 0.1 wt % QDs, FIG. 1198) and 20%
(LSC20, 0.2 wt % QDs, FIG. 20) of the incident solar power. The
concentrators were illuminated perpendicular to their surface (area
A.sub.LSC=12 cm.times.12 cm=144 cm.sup.2) by a calibrated solar
simulator with power density I=100 mW/cm.sup.2 (1.5 AM Global). The
light radiated from the edges of the waveguide was collected using
calibrated silicon photodiodes installed along the slab perimeter
(area A.sub.edge=48 cm.times.0.3 cm=14.4 cm.sup.2). In order to
reproduce the situation of a PV window exposed to sunlight, no
reflector was placed at the bottom of the slabs. The optical power
conversion efficiency was calculated using the expression:
.eta.=P.sub.OUT/P.sub.IN, where P.sub.OUT is the luminous power
collected by the photodiodes and P.sub.IN is the solar power
incident onto the LSC surface. Based on these measurements, a value
of .eta.=1.02% was obtained for LSC10 and .eta.=3.27% for LSC20.
These results were particularly remarkable considering that both
samples exhibited a high degree of transparency across the visible
spectrum.
[0142] Another property of these LSCs, which benefits their
application as building integrated PVs, is that they do not
introduce a significant distortion to the spectrum of solar
radiation, that is, behave as uncolored, neutral density filters.
This property was qualitatively illustrated by taking photographs
of a color-rich scene (tulip field) either without any filtering
(FIG. 21A) or with LSC10 (FIG. 21B) or LSC20 (FIG. 21C) placed in
front of the camera lens. It can be clearly seen that neither of
the LSC samples introduced any apparent color distortions; a small
effect of a denser LSC20 sample was a slight accentuation of warm
color tones. These pictures were taken exclusively to highlight the
color filtering effect of the LSCs and not their absolute
attenuation factor. FIGS. 22A and 22B provide an estimation of the
light attenuation effect of the devices. FIGS. 22A and 22B are
photographs taken with fixed exposure time and aperture of a white
scattering background, and with filtering half of the field of view
with LSC10 (FIG. 22A) and LSC20 (FIG. 22B).
[0143] In order to quantify both the color appearance of our
devices and their effects on color perception, and to further
emphasize the difference with respect to traditional colored LSCs,
side-by-side colorimetry evaluations were performed on LSC20 and on
an LSC based on Crs040 Yellow, a typical large Stokes-shift organic
emitter, fabricated so as to exhibit the same total absorbance
across the whole solar spectrum (about 20%). FIG. 23A provides a
photograph of the LSC based on Crs040 Yellow. FIG. 23B is a
photograph of a reflecting white background taken with the same
camera filtering half of the field of view with the Crs040-LSC.
FIG. 23C is a color rendering index (CRI) plot of original Munsell
test color samples (TCS) under D65 reference illuminant before
(white dots) and after chromatic adaptation by the same LSC,
illustrating that the total color rendering index R.sub.a is
56.6.
[0144] The chromatic coordinates in CIE L*a*b* (Commission
Internationale de le Eclairage) color space of the LSC20 and
Crs040-LSC are shown in FIG. 24. FIG. 25 provides the reflectance
spectra of LSC20 and the LSC incorporating Crs040 Yellow dye
collected using an integrating sphere, and placing a
Spectralon.RTM. scatterer on the back side of the LSCs, following
the conventional procedure for colorimetric measurements on
semitransparent materials. LSC20 exhibited color coordinates
L*=56.6, a*=5.1 and b*=32.1, which placed it in the dark brown
range of Munsell's color atlas, while the LSC incorporating Crs040
had L*=90.7, a*=3.3 and b*=55.3, corresponding to Munsell brilliant
yellow color. In addition to potentially imposing aesthetic
constraints to the architectural applicability of LSC technology,
color also may determine the type and entity of alteration of the
color perception LSCs might cause in individuals living in
buildings with LSC-based PV glazing systems. Specifically, partial
absorption of the incident solar spectrum by semitransparent
colored LSCs may reduce the color rendering index of natural
sunlight, resulting in altered colors of indoor settings. In
addition, looking through colored LSCs windows may result in
filtered chromatic perception of outdoor spaces, with an effect
that can be assimilated to artificially induced color blindness
(FIGS. 21A-21C). FIG. 26 illustrates the color coordinates (CIE
1960 Uniform Color Space) of original Munsell test color samples
(TCS) under D65 (noon daylight) reference illuminant before and
after spectral adaptation by LSC20. Remarkably, the coordinates for
each TCS illuminated with filtered light are very close to those
measured with the unfiltered illuminant, resulting in a total color
rendering index R.sub.a=90.7, corresponding to CIE color rendering
group 1A, which fulfills the highest requirements for indoor
illumination (typical applications: galleries, medical
examinations, color mixing) and further confirms the color
neutrality of our LSCs based on CISeS QDs. For direct comparison,
the LSC based on Crs040 Yellow dye has R.sub.a=56.6, corresponding
to CIE group 3 (suitable for industrial illumination, see FIG.
23C).
[0145] To evaluate the potential alteration of indoor-to-outdoor
chromatic perception that could be caused by using the disclosed
LSCs as semitransparent PV glazing, Farnsworth-Munsell 100 hue
color vision tests were performed on 40 non-color blind subjects
between 20 and 55 years of age. In order to account for individual
differences in color sensitivity across the whole statistic
population, the test was repeated for each subject in identical
conditions both without any filter, and by filtering the subject's
vision using LSC20 or Crs040-LSCs. The histogram of the total error
score (TES) obtained by the tested subjects is reported in FIG. 27,
sorted in ascending order by the TES value without filtering (note
that the order of tests in the three conditions was chosen randomly
across the population to avoid results to be biased by learning
effects). By using LSC20, all tested subjects obtained total error
scores, TES<70 (median: <TES.sub.LSC20>=38 vs.
<TES.sub.No Filter>=20), corresponding to normal color
vision. In contrast, Crs040-LSCs results in significant color
distortion (<TES.sub.Crs040>=156), leading to various degrees
of induced color blindness.
[0146] It is unclear whether the large Stokes shift .DELTA.s is an
`apparent` or `true` Stoke shift. It can be seen that the
absorption spectrum does not fall off sharply past the peak on its
low-energy side, but instead shows a long tail, which extend to the
center of the PL band (see FIGS. 7, 9 and 13). Such behavior is
typical of, for example, Si and Ge QDs or type-II
hetero-nanocrystals. In these structures, the band-edge transition
is weak as it is indirect either in the momentum or in real space,
which leads to the development of a large apparent Stokes shift
defined by the energy spacing between the PL band and the first
higher-energy strong (typically, direct) optical transition.
However, a large Stokes shift could be insufficient to ensure a
significant suppression of re-absorption, as a large width of
spectral features can still result in considerable overlap between
the low-energy tail of the absorption spectrum and the emission
profile. In organic molecules in diluted liquid or solid solutions,
the spectral linewidth is typically determined by conformational
disorder, while, in QDs inhomogeneous broadening is typically due
to sample polydispersity. This is the case for CISeS QDs that show
residual overlap between emission and absorption bands that can, in
principle, be reduced by improving the uniformity of QD sizes.
[0147] To investigate the light emission mechanism and the nature
of a large Stokes shift in I-III-VI.sub.2 QDs, spectroscopic
studies were performed on QDs of pure CIS composition. In these
QDs, the wavelengths of both band-edge absorption and emission fell
within the visible spectral range, which can be accessed
experimentally using a combination of time-resolved PL and TA
techniques. The analysis conducted for CIS QDs should be applicable
to CISeS QDs of arbitrary formulations as the main effect of
incorporation of Se is lowering PL and absorption energies as a
result of the reduced band gap. FIG. 28 illustrates the absorption
and emission spectra of a representative CIS QD sample together
with its PL excitation (PLE) spectrum collected at the peak PL
wavelength. The PL band was centered at 600 nm (2.06 eV), while the
first discernible absorption feature was at 500 nm (2.48 eV), which
corresponded to a Stokes shift of 410 meV. The PLE spectrum was
identical to the absorption spectrum, indicating that the PL was
excited via intrinsic electronic transitions of the ternary
semiconductor. There was a small yet measurable shift of the PLE
spectra collected on the blue and on the red tail of the PL
spectrum (555 nm and 655 nm, FIG. 29), which further supported the
role of sample polydispersity in determining the emission
linewidth. To verify that the absorption peak did correspond to the
band-edge transition, TA studies were conducted, in which changes
in optical absorption induced by a short 3 eV, 100 fs pump pulse
were monitored, with a broad-band probe pulse of a white-light
super-continuum. The measured TA spectra were dominated by a
bleaching band located exactly at the position of the absorption
peak (about 500 nm) (FIG. 30). At low excitation fluences, when the
number of photons absorbed per QD per pulse (<N>) was less
than unity, this peak remained almost unchanged up to the longest
pump-probe delays used in these measurements (.about.500 ps). FIG.
31 shows the pump-intensity dependence of TA decay in CIS QDs
measured at 500 nm (2.48 eV) under excitation with 100 fs, 3.1 eV
frequency doubled pulses from an amplified Ti:sapphire laser. The
excitation level is shown on the right in terms of the number of
photons absorbed per QD per pulse, <N>. This indicated that
it is indeed due to saturation (Pauli blocking) of band-edge states
where carriers accumulate following intra-band relaxation.
[0148] In the case of state filling, the TA amplitude is directly
proportional to the sum of the occupation factors of the electron
and hole states involved in the optical transition probed in the
experiment. Because of large hole effective masses and the complex
multi-sub-band structure of the valence band, the density of hole
states in I-III-VI.sub.2 QDs is much higher than that of the
electron states. As a result, single-state occupation factors of
valence-band levels are much lower than those of conduction-band
levels and hence the TA amplitude is dominated by the contribution
from the electrons. This situation is similar to that realized in
QDs of II-VI semiconductors such as CdSe where the band-edge bleach
has been routinely used to elucidate population build-up and decay
of the 1S electron state. Thus the TA studies confirmed that the
500 nm (2.45 eV) feature observed in linear absorption marked the
position of the QD band edge and hence a large separation between
this feature and the PL band is a "true" and not just an apparent
Stokes shift. This further indicated that highly efficient emission
from CIS QDs did not arise from the band edge transition but rather
was due to a radiative transition involving the band-edge electron
level and an intra-gap hole state.
[0149] A survey of numerous literature reports indicated a
remarkable consistency in the position of the PL band between CIS
QD samples prepared by different chemical approaches, which
suggested that the hole-like defect responsible for intra-gap
emission was likely native to this material's system. One
possibility suggested by recent magneto-PL studies is that the
intra-gap hole state is associated with the Cu.sup.2+ ion, which is
a common substitutional impurity in II-VI semiconductor where it
creates a fairly deep acceptor level. In structural terms,
I-III-VI.sub.2 semiconductors are ternary analogs of II-VI
materials, and their unit cell can be thought of as being comprised
of two zinc-blende unit cells distorted along the c-axis.
Therefore, it is reasonable to assume that substitutional Cu.sup.2+
impurities can also occur in I-III-VI.sub.2 semiconductors. Based
on charge balance considerations, one can think of two Cu.sup.2+
ions replacing Cu.sup.1+ and In.sup.3+ in adjacent sub-cells or
Cu.sup.2+ paired with a Cu.sup.+1 vacancy, which is a well-known
defect in bulk I-III-VI.sub.2 materials.
[0150] In conclusion, high efficiency large-area LSCs with reduced
re-absorption losses based on heavy-metal free IR emitting
I-III-VI.sub.2 colloidal QDs in a mass polymerized plastic matrix
have been demonstrated. The optical transition responsible for
light emission in these QDs involves an intra-gap hole states,
which leads to a large (ca. 400-500 meV) Stokes shift and greatly
reduced losses to re-absorption. By overcoating QDs with a shell of
wide gap ZnS, the light emission properties of the QDs were
preserved during the entire procedure of their encapsulation into a
polymer matrix. Use of these QDs allows many of previous
limitations of both organic dyes and colloidal QDs to be overcome,
including strong coloring of the LSC and an incomplete coverage of
the solar spectrum, which limited the light collection efficiency.
As a result, an optical power conversion efficiency of up to 3.2%
was obtained, which is the highest reported value for large-area
LSCs. Furthermore, the disclosed devices are essentially colorless
and do not introduce any significant spectral distortion to
transmitted sunlight, which is beneficial for applications such as
tinted PV windows.
[0151] In some embodiments, the disclosed composition is a
substantially transparent composition according to one or more of
the following statements:
[0152] 1. A substantially transparent composition, comprising:
[0153] a transparent matrix; and plural, substantially
non-aggregated heavy metal free nanocrystals substantially
homogeneously dispersed in the transparent matrix and separated by
a distance greater than an energy transfer distance.
[0154] 2. The composition of statement 1, wherein the heavy metal
free nanocrystals do not comprise cadmium.
[0155] 3. The composition of statement 1 or statement 2, wherein
the heavy metal free nanocrystals do not comprise cadmium, mercury,
arsenic or lead.
[0156] 4. The composition of any one of statements 1-3, wherein the
heavy metal free nanocrystals comprise a core and at least one
shell.
[0157] 5. The composition of statement 4, wherein the nanocrystal
core has an intrinsically large Stokes shift.
[0158] 6. The composition of statement 5, wherein the shell does
not substantially affect the Stokes shift of the nanocrystal.
[0159] 7. The composition of statement 4, wherein the shell
comprises a shell material and the shell material is selected to
enhance the stability of the core, to enable the nanocrystals to be
dispersed in a matrix without substantially quenching the quantum
yield of the nanocrystals, maintain or improve the photoluminescent
intensity of the nanocrystal or a combination thereof.
[0160] 8. The composition of any one of statements 1-7, wherein the
transparent matrix is a matrix transparent to visible light, IR
light, UV light, or a combination thereof.
[0161] 9. The composition of any one of statements 1-8, wherein the
transparent matrix is a polymer matrix, sol-gel matrix, glass
matrix, solvent matrix or combination thereof.
[0162] 10. The composition of statement 9, wherein the transparent
matrix is a polymer matrix.
[0163] 11. The composition of statement 10, wherein the polymer
matrix comprises a polymer selected from poly acrylate, poly
methacrylate, polyolefin, poly vinyl, epoxy resin, polycarbonate,
polyacetate, polyamide, polyurethane, polyketone, polyester,
polycyanoacrylate, silicone, polyglycol, polyimide, fluorinated
polymer, polycellulose, poly oxazine or combinations thereof.
[0164] 12. The composition of statement 10 or statement 11, wherein
the polymer matrix comprises an acrylate polymer.
[0165] 13. The composition of statement 12, wherein the acrylate
polymer is made from an acrylate monomer selected from methyl
acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, pentyl
acrylate, hexyl acrylate, octyl acrylate, nonyl acrylate, decyl
acrylate dodecyl acrylate, 2-chloroethyl acrylate, methyl
methacrylate, ethyl methacrylate, butyl methacrylate, pentyl
methacrylate, hexyl methacrylate, octyl methacrylate, nonyl
methacrylate, decyl methacrylate, lauryl methacrylate, 2-ethylhexyl
acrylate, hydroxyethyl methacrylate, trimethylolpropane triacrylate
or a combination thereof.
[0166] 14. The composition of statement 12, wherein the acrylate
polymer comprises polylauryl methacrylate.
[0167] 15. The composition of any one of statements 1-14, wherein
the nanocrystal comprises zinc sulfide (ZnS), zinc selenide (ZnSe),
zinc oxide (ZnO), zinc telluride (ZnTe), aluminum nitride (AlN),
aluminum sulfide (AlS), aluminum phosphide (AlP), aluminum
antimonide (AlSb), gallium nitride (GaN), gallium phosphide (GaP),
gallium antimonide (GaSb), indium nitride (InN), indium phosphide
(InP), indium antimonide (InSb), thallium nitride (TlN), thallium
phosphide (TlP), thallium antimonide (TlSb), indium gallium nitride
(InGaN), indium gallium phosphide (InGaP), aluminum indium nitride
(AlInN), indium aluminum phosphide (InAlP), aluminum gallium
phosphide (AlGaP), aluminum indium gallium nitride (AlInGaN),
silver indium selenide sulfide (AgInSe.sub.xS.sub.2-x), gold indium
selenide sulfide (AuInSe.sub.xS.sub.2-x), copper aluminum selenide
sulfide (CuAlSe.sub.xS.sub.2-x), copper gallium selenide sulfide
(CuGaSe.sub.xS.sub.2-x), silver indium selenide (AgInSe.sub.2),
gold indium sulfide (AuInS.sub.2), copper aluminum selenide
(CuAlSe.sub.2), copper gallium selenide (CuGaSe.sub.2), copper
indium selenide sulfide (CuInSe.sub.xS.sub.2-x), Si, Ge, Sn, SiGe,
SiSn, GeSn, aluminum (Al), gold (Au), silver (Ag), cobalt (Co),
iron (Fe), nickel (Ni), copper (Cu), gallium, silicon, manganese
(Mn), indium, selenium, sulfur or combinations thereof.
[0168] 16. The composition of any one of statements 1-15, wherein
the nanocrystal comprises InSb, InP, Ge, Si, Sn, Sn, InN, AlN, GaN,
ZnTe, ZnSe, ZnS, ZnO, AgInSe.sub.xS.sub.2-x, AuInSe.sub.xS.sub.2-x,
CuAlSe.sub.xS.sub.2-x, CuGaSe.sub.xS.sub.2-x, or
CuInSe.sub.xS.sub.2-x, where x is from 0 to 2, or combinations
thereof.
[0169] 17. The composition of any one of statements 4-16, wherein
the nanocrystal core comprises InSb, InP, Ge, Si, Sn, Sn, InN, AlN,
GaN, ZnTe, ZnSe, ZnS, ZnO, AgInSe.sub.xS.sub.2-x,
AuInSe.sub.xS.sub.2-x, CuAlSe.sub.xS.sub.2-x,
CuGaSe.sub.xS.sub.2-x, or CuInSe.sub.xS.sub.2-x, where x is from 0
to 2, or combinations thereof.
[0170] 18. The composition of any one of statements 4-17, wherein
the nanocrystal shell comprises InSb, InP, Ge, Si, Sn, Sn, InN,
AlN, GaN, ZnTe, ZnSe, ZnS, or ZnO, AgInSe.sub.xS.sub.2-x,
AuInSe.sub.xS.sub.2-x, CuAlSe.sub.xS.sub.2-x,
CuGaSe.sub.xS.sub.2-x, or CuInSe.sub.xS.sub.2-x, or combinations
thereof.
[0171] 19. The composition of any one of statements 4-18, wherein
the nanocrystal has a core/shell structure selected from InP/ZnSe,
InSb/ZnSe, InP/ZnS, InSb/ZnS, Ge/Si, Si/Ge, Sn/Si, Si/Sn, Ge/Sn,
Sn/Ge, AgInSe.sub.xS.sub.2-x/ZnS, AuInSe.sub.xS.sub.2-x/ZnS,
CuAlSe.sub.xS.sub.2-x/ZnS, CuGaSe.sub.xS.sub.2-x/ZnS,
CuInSe.sub.xS.sub.2-x/CuInS.sub.2,
CuInSe.sub.xS.sub.2-x/AuGaS.sub.2, or CuInSe.sub.xS.sub.2-x/ZnS,
where x is from 0 to 2.
[0172] 20. The composition of any one of statements 1-19, wherein
the nanocrystal comprises CuInS.sub.2, CuInSe.sub.0.1S.sub.1.9,
CuInSe.sub.0.2S.sub.1.8, CuInSe.sub.0.25S.sub.1.75,
CuInSe.sub.0.3S.sub.1.7, CuInSe.sub.0.4S.sub.1.6,
CuInSe.sub.0.5S.sub.1.5, CuInSe.sub.0.6S.sub.1.4,
CuInSe.sub.0.7S.sub.1.3, CuInSe.sub.0.75S.sub.1.25,
CuInSe.sub.0.8S.sub.1.2, CuInSe.sub.0.9S.sub.1.1, CuInSeS,
CuInSe.sub.1.1S.sub.0.9, CuInSe.sub.1.2S.sub.0.8,
CuInSe.sub.1.25S.sub.0.75, CuInSe.sub.1.3S.sub.0.7,
CuInSe.sub.1.4S.sub.0.6, CuInSe.sub.1.5S.sub.0.5,
CuInSe.sub.1.6S.sub.0.4, CuInSe.sub.1.7S.sub.0.3,
CuInSe.sub.1.75S.sub.0.25, CuInSe.sub.1.8S.sub.0.2,
CuInSe.sub.1.9S.sub.0.1, CuInSe.sub.2 or a combination thereof.
[0173] 21. The composition of any one of statements 1-20, wherein
the nanocrystals have a shape selected from a sphere, rod,
tetrapod, heteronanorod, hetero-platelet, hetero-tripod,
hetero-tetrapod, hetero-hexapod, dot-in-rod, dot-in-platelet,
rod-in-rod and platelet-in-platelet, dot-in-bulk, complex branched
hetero-structure, or a combination thereof.
[0174] 22. The composition of statement 5, wherein global Stokes
shift is greater than 200 meV.
[0175] 23. The composition of any one of statements 1-22, wherein
the nanocrystal concentration in the transparent matrix of from
greater than zero wt % to 10 wt % relative to the weight of the
transparent matrix.
[0176] 24. The composition of statement 23, wherein the nanocrystal
concentration is from greater than zero wt % to 0.5 wt %.
[0177] 25. The composition of statement 24, wherein the nanocrystal
concentration is from 0.1 wt % to 0.2 wt %.
[0178] 26. The composition of any one of statements 1-25, wherein
the nanocrystals are dispersed in the transparent matrix such than
a nanocrystal emission efficiency drops by less than 10% compared
to a nanocrystal emission efficiency of nanocrystals dissolved in a
solvent.
[0179] 27. The composition of statement 26, wherein the nanocrystal
emission efficiency drops by less than 5%.
[0180] 28. The composition of statement 26, wherein the nanocrystal
emission efficiency drops by less than 1%.
[0181] 29. The composition of any one of statements 1-28, wherein
the composition is substantially colorless.
[0182] 30. The composition of statement 29, wherein the composition
has a color rendering index of from 80 to 100.
[0183] 31. The composition of statement 30, wherein the color
rendering index is from 90 to 100.
[0184] 32. The composition of any one of statements 1-31, wherein
the composition is a composition that absorbs at least 10% of
incident solar light.
[0185] 33. The composition of any one of statements 1-31, wherein
the composition has an optical power conversion ratio of greater
than 1%.
[0186] 34. The composition of any one of statements 1-33, wherein
the nanocrystals have a core/shell structure of
CuInSe.sub.xS.sub.2-x/ZnS, where x is from greater than 0 to less
than 2.
[0187] 35. A composition substantially transparent to visible
light, IR light, UV light, or a combination thereof, the
composition, comprising:
[0188] a polymer matrix wherein the polymer is selected from poly
acrylate, poly methacrylate, polyolefin, poly vinyl, epoxy resin,
polycarbonate, polyacetate, polyamide, polyurethane, polyketone,
polyester, polycyanoacrylate, silicone, polyglycol, polyimide,
fluorinated polymer, polycellulose, poly oxazine or combinations
thereof; and
[0189] plural, substantially non-aggregated heavy metal free
nanocrystals substantially homogeneously dispersed in the polymer
matrix at a concentration of from greater than zero wt % to 1 wt %
relative to the weight of the polymer matrix such that a
nanocrystal emission efficiency drops by less than 10% compared to
a quantum dot emission efficiency of nanocrystals dissolved in a
solvent, the core/shell structure being selected from InP/ZnSe,
InSb/ZnSe, InP/ZnS, InSb/ZnS, Ge/Si, Si/Ge, Sn/Si, Si/Sn, Ge/Sn,
Sn/Ge, AgInSe.sub.xS.sub.2-x/ZnS, AuInSe.sub.xS.sub.2-x/ZnS,
CuAlSe.sub.xS.sub.2-x/ZnS, CuGaSe.sub.xS.sub.2-x/ZnS,
CuInSe.sub.xS.sub.2-x/CuInS.sub.2,
CuInSe.sub.xS.sub.2-x/AuGaS.sub.2, or CuInSe.sub.xS.sub.2-x/ZnS,
where x is from 0 to 2, the nanocrystals having a global Stokes
shift of greater than 200 meV and being separated by a distance
greater than an energy transfer distance;
[0190] wherein the composition has a color rendering index of from
90 to 100.
[0191] Also disclosed herein are embodiments of a device according
to one or more of the following statements:
[0192] 36. A device, comprising a substantially colorless,
transparent composition comprising a transparent matrix comprising
plural, substantially non-aggregated heavy metal free nanocrystals
substantially homogeneously dispersed in the transparent matrix and
separated by a distance greater than an energy transfer distance,
the nanocrystals comprising a core and at least one shell about the
core.
[0193] 37. The device of statement 36, wherein the nanocrystals
dispersed in the transparent matrix have a quantum yield of from
greater than 0 to 90%.
[0194] 38. The device of statement 37, wherein the
photoluminescence quantum yield is from 10% to 80%.
[0195] 39. The device of statement 37, wherein the
photoluminescence quantum yield is from 10% to 50%.
[0196] 40. The device of any one of statements 36-39, wherein the
transparent matrix is a matrix transparent or semi-transparent to
visible light, infrared light, ultraviolet light or a combination
thereof.
[0197] 41. The device of any one of statements 36-40, wherein the
device comprises a transparent substrate at least partially coated
with a film comprising the composition.
[0198] 42. The device of statement 41, wherein the transparent
substrate is a glass substrate.
[0199] 43. The device of any one of statements 36-40, wherein the
device comprised a polymer matric comprising the nanocrystals.
[0200] 44. The device of any one of statements 36-43, further
comprising a photovoltaic.
[0201] 45. The device of any one of statements 36-44, further
comprising a reflector and/or a diffuser.
[0202] 46. The device of any one of statements 36-45, wherein the
device is a window.
[0203] 47. The device of statement 46, wherein the window comprises
at least one window pane comprising the composition.
[0204] 48. The device of statement 46, wherein the window comprises
at least one window pane at least partially coated with a film
comprising the composition.
[0205] 49. The device of statement 46, wherein the window comprises
at least two window panes and the composition is positioned between
the window panes.
[0206] 50. The device according to statement 36 wherein the
composition comprises:
[0207] a polymer matrix wherein the polymer is selected from poly
acrylate, poly methacrylate, polyolefin, poly vinyl, epoxy resin,
polycarbonate, polyacetate, polyamide, polyurethane, polyketone,
polyester, polycyanoacrylate, silicone, polyglycol, polyimide,
fluorinated polymer, polycellulose, poly oxazine or combinations
thereof; and
[0208] plural, substantially non-aggregated heavy metal free
nanocrystals substantially homogeneously dispersed in the polymer
matrix at a concentration of from greater than zero wt % to 1 wt %
relative to the weight of the polymer matrix such that a
nanocrystal emission efficiency drops by less than 10% compared to
a nanocrystal emission efficiency of nanocrystals dissolved in a
solvent, the core/shell structure being selected from InP/ZnSe,
InSb/ZnSe, InP/ZnS, InSb/ZnS, Ge/Si, Si/Ge, Sn/Si, Si/Sn, Ge/Sn,
Sn/Ge, AgInSe.sub.xS.sub.2-x/ZnS, AuInSe.sub.xS.sub.2-x/ZnS,
CuAlSe.sub.xS.sub.2-x/ZnS, CuGaSe.sub.xS.sub.2-x/ZnS,
CuInSe.sub.xS.sub.2-x/CuInS.sub.2,
CuInSe.sub.xS.sub.2-x/AuGaS.sub.2, or CuInSe.sub.xS.sub.2-x/ZnS,
where x is from 0 to 2, the nanocrystals having a global Stokes
shift of greater than 200 meV and being separated by a distance
greater than an energy transfer distance.
[0209] 51. The device of any one of statements 36-50, wherein the
nanocrystals have a core/shell structure of
CuInSe.sub.xS.sub.2-x/ZnS, where x is from 0 to 2.
[0210] 52. The device of statement 51, wherein the nanocrystal core
comprises CuInS.sub.2, CuInSe.sub.0.2S.sub.1.8,
CuInSe.sub.0.25S.sub.1.75, CuInSe.sub.0.3S.sub.1.7,
CuInSe.sub.0.4S.sub.1.6, CuInSe.sub.0.5S.sub.1.5,
CuInSe.sub.0.6S.sub.1.4, CuInSe.sub.0.7S.sub.1.3,
CuInSe.sub.0.75S.sub.1.25, CuInSe.sub.0.8S.sub.1.2,
CuInSe.sub.0.9S.sub.1.1, CuInSeS, CuInSe.sub.0.1S.sub.0.9,
CuInSe.sub.1.2S.sub.0.8, CuInSe.sub.1.25S.sub.0.75,
CuInSe.sub.1.3S.sub.0.7, CuInSe.sub.1.4S.sub.0.6,
CuInSe.sub.1.5S.sub.0.5, CuInSe.sub.1.6S.sub.0.4,
CuInSe.sub.1.7S.sub.0.3, CuInSe.sub.1.75S.sub.0.25,
CuInSe.sub.1.8S.sub.0.2, CuInSe.sub.1.9S.sub.0.1, CuInSe.sub.2 or a
combination thereof.
[0211] 53. The device of any one of statements 36-52, wherein the
device has a color rendering index of from 80 to 100.
[0212] 54. A building or transportation device having at least one
window comprising a substantially colorless composition comprising
a transparent matrix and plural, substantially non-aggregated heavy
metal free nanocrystals substantially homogeneously dispersed in
the transparent matrix and separated by a distance greater than an
energy transfer distance, the nanocrystals comprising a core and at
least one shell about the core.
[0213] 55. The building or transportation device according to
statement 54 wherein the composition comprises:
[0214] a polymer matrix wherein the polymer is selected from poly
acrylate, poly methacrylate, polyolefin, poly vinyl, epoxy resin,
polycarbonate, polyacetate, polyamide, polyurethane, polyketone,
polyester, polycyanoacrylate, silicone, polyglycol, polyimide,
fluorinated polymer, polycellulose, poly oxazine or combinations
thereof; and
[0215] plural, substantially non-aggregated heavy metal free
nanocrystals substantially homogeneously dispersed in the polymer
matrix at a concentration of from greater than zero wt % to 1 wt %
relative to the weight of the polymer matrix such that a
nanocrystal emission efficiency drops by less than 10% compared to
a quantum dot emission efficiency of nanocrystals dissolved in a
solvent, the core/shell structure being selected from InP/ZnSe,
InSb/ZnSe, InP/ZnS, InSb/ZnS, Ge/Si, Si/Ge, Sn/Si, Si/Sn, Ge/Sn,
Sn/Ge, AgInSe.sub.xS.sub.2-x/ZnS, AuInSe.sub.xS.sub.2-x/ZnS,
CuAlSe.sub.xS.sub.2-x/ZnS, CuGaSe.sub.xS.sub.2-x/ZnS,
CuInSe.sub.xS.sub.2-x/CuInS.sub.2,
CuInSe.sub.xS.sub.2-x/AuGaS.sub.2, or CuInSe.sub.xS.sub.2-x/ZnS,
where x is from 0 to 2, the nanocrystals having a global Stokes
shift of greater than 200 meV and being separated by a distance
greater than an energy transfer distance.
[0216] 56. The device of statement 55, wherein the nanocrystals
have a core/shell structure of CuInSe.sub.xS.sub.2-x/ZnS, where x
is from 0 to 2.
[0217] 57. The device of statement 56, wherein the nanocrystal core
comprises CuInS.sub.2, CuInSe.sub.0.2S.sub.1.8,
CuInSe.sub.0.25S.sub.1.75, CuInSe.sub.0.3S.sub.1.7,
CuInSe.sub.0.4S.sub.1.6, CuInSe.sub.0.5S.sub.1.5,
CuInSe.sub.0.6S.sub.1.4, CuInSe.sub.0.7S.sub.1.3,
CuInSe.sub.0.75S.sub.1.25, CuInSe.sub.0.8S.sub.1.2,
CuInSe.sub.0.9S.sub.1.1, CuInSeS, CuInSe.sub.0.0S.sub.0.9,
CuInSe.sub.1.2S.sub.0.8, CuInSe.sub.1.25S.sub.0.75,
CuInSe.sub.1.3S.sub.0.7, CuInSe.sub.1.4S.sub.0.6,
CuInSe.sub.1.5S.sub.0.5, CuInSe.sub.1.6S.sub.0.4,
CuInSe.sub.1.7S.sub.0.3, CuInSe.sub.1.75S.sub.0.25,
CuInSe.sub.1.8S.sub.0.2, CuInSe.sub.1.9S.sub.0.1, CuInSe.sub.2 or a
combination thereof.
[0218] 58. The building or transportation device according to any
one of statements 54-57, wherein the transportation device is an
automobile, ship or airplane.
[0219] Additionally, disclosed herein are embodiments of a method,
according to one or more of the following statements:
[0220] 59. A method for making a composition, comprising:
[0221] dispersing heavy metal free nanocrystals in a first amount
of a monomer and a first polymerization initiator to form a
dispersion of quantum dots in monomer;
[0222] mixing the dispersion of quantum dots in monomer with a
second amount of the monomer and an initiator to form a
mixture;
[0223] agitating the mixture; and
[0224] initiating polymerization of the monomer to form the
composition comprising a transparent matrix with quantum dots
dispersed within.
[0225] 60. The method of statement 59, wherein the transparent
matrix comprises a polymer selected from poly acrylate, poly
methacrylate, polyolefin, poly vinyl, epoxy resin, polycarbonate,
polyacetate, polyamide, polyurethane, polyketone, polyester,
polycyanoacrylate, silicone, polyglycol, polyimide, fluorinated
polymer, polycellulose, poly oxazine or combinations thereof.
[0226] 61. The method of statement 60, wherein the monomer is an
acrylate monomer.
[0227] 62. The method of statement 61, wherein the acrylate monomer
is selected from methyl acrylate, ethyl acrylate, propyl acrylate,
butyl acrylate, pentyl acrylate, hexyl acrylate, octyl acrylate,
nonyl acrylate, decyl acrylate dodecyl acrylate, 2-chloroethyl
acrylate, methyl methacrylate, ethyl methacrylate, butyl
methacrylate, pentyl methacrylate, hexyl methacrylate, octyl
methacrylate, nonyl methacrylate, decyl methacrylate, lauryl
methacrylate, 2-ethylhexyl acrylate, hydroxyethyl methacrylate,
trimethylolpropane triacrylate or a combination thereof.
[0228] 63. The method of statement 61, wherein the acrylate monomer
comprises lauryl methacrylate.
[0229] 64. The method of any one of statement 59-63, wherein the
initiator is a radical initiator, and initiating polymerization
comprises irradiating the mixture.
[0230] 65. The method of any one of statements 59-64, wherein the
initiator is 2,2-dimethoxy-1,2-diphenylethan-1-one.
[0231] 66. The method of any one of statements 59-65, wherein the
mixture further comprises a cross-linking agent.
[0232] 67. The method of statement 66, wherein the cross-linking
agent comprises ethylene glycol dimethacrylate.
[0233] 68. The method of any one of statements 59-67, wherein
agitating the mixture comprises stirring the mixture, sonicating
the mixture, shaking the mixture, or a combination thereof.
[0234] 69. The method of any one of statements 59-68, further
comprising allowing the polymerization to proceed in the dark.
[0235] Furthermore, disclosed herein are embodiments of a product
according to one or more of the flowing statements:
[0236] 70. A product made by any of method statements 59-59.
[0237] 71. The product according to statement 70 wherein the
product is a window.
[0238] 72. The product according to statement 71 wherein the window
is in a building or transportation device.
[0239] In view of the many possible embodiments to which the
principles of the disclosed invention may be applied, it should be
recognized that the illustrated embodiments are only preferred
examples of the invention and should not be taken as limiting the
scope of the invention. Rather, the scope of the invention is
defined by the following claims. We therefore claim as our
invention all that comes within the scope and spirit of these
claims.
* * * * *