U.S. patent application number 14/328004 was filed with the patent office on 2014-10-30 for optoelectronic devices with all-inorganic colloidal nanostructured films.
This patent application is currently assigned to Sunpower Technologies LLC. The applicant listed for this patent is Sunpower Technologies LLC. Invention is credited to Daniel Landry.
Application Number | 20140319525 14/328004 |
Document ID | / |
Family ID | 51135649 |
Filed Date | 2014-10-30 |
United States Patent
Application |
20140319525 |
Kind Code |
A1 |
Landry; Daniel |
October 30, 2014 |
OPTOELECTRONIC DEVICES WITH ALL-INORGANIC COLLOIDAL NANOSTRUCTURED
FILMS
Abstract
Optoelectronic devices and methods of producing the same are
disclosed. Methods may include forming a film from fused
all-inorganic colloidal nanostructures, where the nanostructures
may include inorganic nanoparticles and functional inorganic
ligands, and the fused nanostructures may form an electrical
network that is photoconductive. Other methods may provide an
optoelectronic device which may include an integrated circuit or
large panel thin-film transistor matrix, an array of conductive
regions, and an optically sensitive material over at least a
portion of the integrated circuit and in electrical communication
with at least one conductive region of the array of conductive
regions.
Inventors: |
Landry; Daniel; (Redondo
Beach, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sunpower Technologies LLC |
San Marcos |
CA |
US |
|
|
Assignee: |
Sunpower Technologies LLC
San Marcos
CA
|
Family ID: |
51135649 |
Appl. No.: |
14/328004 |
Filed: |
July 10, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13755186 |
Jan 31, 2013 |
8779413 |
|
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14328004 |
|
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61744953 |
Oct 9, 2012 |
|
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Current U.S.
Class: |
257/53 |
Current CPC
Class: |
H01L 31/00 20130101;
H01L 27/14669 20130101; H01L 31/035218 20130101; H01L 27/14676
20130101; H01L 27/14665 20130101; H01L 31/0296 20130101; H01L
31/0304 20130101; Y02E 10/50 20130101; H01L 31/0376 20130101 |
Class at
Publication: |
257/53 |
International
Class: |
H01L 27/146 20060101
H01L027/146; H01L 31/0304 20060101 H01L031/0304; H01L 31/0376
20060101 H01L031/0376; H01L 31/0296 20060101 H01L031/0296 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 2013 |
US |
PCT/US2013/062541 |
Claims
1. A film comprising a nanostructure comprising an inorganic
nanoparticle fused with a functional inorganic ligand.
2. The film of claim 1, wherein the nanostructure is devoid of
organic material.
3. The film of claim 1, wherein charge carriers are mobile
throughout the film.
4. The film of claim 1, wherein the nanostructure is fused with a
second nanostructure.
5. The film of claim 4, wherein charge carriers are mobile between
the nanostructure and the fused second nanostructure.
6. The film of claim 4, wherein the fused nanostructures define a
conductive electrical network.
7. The film of claim 4, wherein the fused nanostructures include at
least one functional inorganic ligand selected from a group
consisting of polyatomic anions, transition metals, lanthanides,
actinides, chalcogenide molecular compounds, Zintl ions, inorganic
complexes, metal-free inorganic ligands, and/or a combination
thereof
8. The film of claim 4, wherein fused nanostructures include
nanoparticles of different compositions and fused functional
inorganic ligands.
9. The film of claim 4, wherein fused nanostructures includes
nanoparticles of different sizes and fused functional inorganic
ligands.
10. The film of claim 4, wherein the fused nanostructures have a
carrier mobility of between about 0.01 and about 80
cm.sup.2/Vs.
11. The film of claim 4, wherein the fused nanostructures have a
substantially linear response to irradiation in at least a portion
of the electromagnetic spectrum.
12. The film of claim 1, wherein fused nanostructures have an
electrical resistance of at least about 25 k-Ohm/square.
13. The film of claim 1, wherein the film has an optical response
to irradiation in at least one of the x-ray, ultraviolet, visible,
and/or infrared regions of the electromagnetic spectrum.
14. The film of claim 1, wherein the film is substantially
inorganic.
15. The film of claim 1, wherein the inorganic nanoparticles and
functional inorganic ligands are colloidal and included in an ink
or solution that is deposited and fused, and wherein the film
retains the inorganic nanoparticles and functional inorganic
ligands.
16. The film of claim 1, wherein the inorganic nanoparticles
maintain the same size, shape, and opto-electronic properties of
the inorganic nanoparticles that were deposited from the
all-inorganic nanostructure ink.
17. The film of claim 1, wherein the inorganic nanoparticles
include semiconductor, metal, metal-oxide, oxide and/or magnetic
alloy materials and/or a combination thereof.
18. The film of claim 1, wherein the inorganic nanoparticles
comprise at least one of PbS, InAs, InP, PbSe, CdS, CdSe, InGaAs,
(Cd-Hg)Te, ZnSe(PbS), ZnS(CdSe), ZnSe(CdS), PbO(PbS), and
PbSO(PbS).
19. The film of claim 1, wherein the optical response of the film
is determined by a size and composition of the inorganic
nanoparticles in the film.
20. The film of claim 1, wherein the film is disposed on a
substrate.
21. The film of claim 20, wherein the substrate is flexible and
formed in a non-planar shape.
22. The film of claim 20, wherein the substrate comprises an
integrated circuit and/or a thin-film transistor array, at least
some components of which are in electrical communication with the
film.
23. The film of claim 20, wherein the substrate comprises at least
one of a semiconducting organic molecule, a semiconducting polymer,
a nanocrystalline semiconductor, an amorphous semiconductor, or a
crystalline semiconductor.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 13/755,186, entitled "OPTOELECTRONIC DEVICES
WITH ALL-INORGANIC COLLOIDAL NANOSTRUCTURED FILMS," filed Jan. 31,
2013, which is claims priority under 35 U.S.C. .sctn.119 to U.S.
Provisional Patent Application Ser. No. 61/744,953, entitled
"OPTOELECTRONIC DEVICES WITH ALL-INORGANIC COLLOIDAL NANOSTRUCTURED
FILMS," filed on Oct. 1, 2012, all of which are hereby incorporated
by reference in their entirety.
BACKGROUND
[0002] 1. Technical Field
[0003] The present disclosure relates in general to optical and
electronic devices, and more particularly, to fused films of
all-inorganic colloidal semiconductor nanometer scale materials
("nanostructures") including semiconductor nanoparticles and
functional inorganic ligands, which may be employed in an
optoelectronic device.
[0004] 2. Background Information
[0005] Digital imaging of sensed electromagnetic wavelengths is
widely used in medical, military, industrial, and scientific
applications. Image sensors include arrays of pixelated
semiconductors and/or active pixel arrays that are optically
sensitive to light (or wavelengths of electromagnetic radiation)
and convert the incident photons to electrons. These photodetectors
are integrated in circuit, and with other electronic circuits to
convert optical signals to electronic signals, to store charge
accumulated by the pixels, to transfer the charge and/or signals
from the array, to convert the analog into digital signals, and to
process digital data to form still or video digital images.
[0006] Examples of image sensors include devices that use silicon
for sensing, read-out electronics, and multiplexing functions. In
some image sensors, optically sensitive silicon photodetectors and
electronics are formed on the same single silicon wafer. In other
examples, larger area, flat panel image sensors consist of a large
array of pixels as part of an active matrix where each pixel has a
thin-film transistor (TFT) that can be externally addressed.
Existing TFT array architectures can be used for larger area image
sensing, however, they cannot tolerate the high temperature
deposition techniques for many photodetecting semiconductor
materials.
[0007] Deposition techniques for certain compound semiconductor
materials are not compatible with established silicon integrated
circuits. In such systems a silicon electronic read-out array and
wavelength radiation sensitive photodetector arrays are fabricated
separately, resulting in a complex assembly procedure, low yield,
poor resolution and higher manufacturing and assembling costs. In
addition, traditional manufacture of semiconductor substrates and
optically sensitive semiconductor layers are limited to rigid and
relatively small area optoelectronic devices.
[0008] Prior methods for solution-based nanoparticle films include
volume losses of 30% or higher which may leave voids, holes, cracks
and other defects in the film that negatively affect optoelectronic
performance and require post-treatment to repair. All-inorganic
colloidal nanostructures including semiconducting nanoparticles can
be processed in solution and/or included in inks that can be
deposited on a suitable substrate. This solution-processing
compatibility allows post-processing atop other integrated
circuits. In addition, the fabrication of optically active films
using all-inorganic colloidal nanostructure inks can be achieved at
low temperature to accommodate additional device structures
including existing and new TFT and organic substrate, and
integrated circuit materials.
[0009] In conventional methods, long-chain, organic ligands that
are linked to nanoparticles are exchanged for shorter organic or
volatile organic or inorganic ligands that are vaporized during a
subsequent heating (annealing, sintering) step to provide a film
consisting mainly of nanoparticles and being substantially free of
ligands. In other conventional methods, the nanoparticle ligands
may be removed by soaking the deposited layers in a solvent that
dissolves and thus dissociates the ligands from the nanoparticles.
These methods may often result in poor fused film qualities that
are not preferential for use in optoelectronic devices, because
organic ligand materials may not be removed once the nanoparticle
solutions are deposited and organic ligand materials act as
insulating materials in the fused films.
[0010] It would be desirable to improve existing methods for
producing optoelectronic devices with all-inorganic colloidal
nanostructures.
SUMMARY
[0011] Embodiments of the present disclosure provide methods for
manufacturing fused films for optoelectronic devices. The fused
film may incorporate an all-inorganic colloidal nanostructured
layer. In addition, the all-inorganic colloidal nanostructured
layer may include semiconductor nanoparticles that may be processed
in a solution and formed into inks
[0012] Nanocrystals may be synthesized in order to create the ink
that may be thermally treated to form the fused film. During
nanocrystal synthesis, semiconductor nanoparticles may be produced
by known techniques such as batch or continuous flow wet chemistry
processes. Semiconductor nanoparticles may include spherical
nanometer-scale, crystalline materials and other shaped
nanometer-scale, crystalline particles such as oblate and oblique
spheroids, rods, wires, the like and combinations thereof. The
semiconductor nanoparticles may include metal, semiconductor,
oxide, metal-oxides and ferromagnetic compositions.
[0013] After nanocrystal synthesis, the semiconductor nanoparticles
may be subject to ligand exchange where organic ligands may be
substituted with pre-selected, functional inorganic ligands. The
exchange and extraction of organic ligands may provide a solution
or ink of all-inorganic colloidal nanostructures (including
functional inorganic ligands and inorganic nanoparticles) that is
substantially free of the organic materials. In some embodiments,
the ligand exchange may involve precipitating the as-synthesized
semiconductor nanoparticles from their original solution, washing,
and re-dispersing in a liquid or solvent which either is or
includes the ligands to be substituted onto the semiconductor
nanoparticles and so completely disassociates the original ligands
from the outer surfaces of the semiconductor nanoparticles and
links the functional inorganic ligands to the semiconductor
nanoparticles.
[0014] The functional inorganic ligands may maintain the stability
of semiconductor nanoparticles in the solution and provide
preferred ordering and close-packing of the semiconductor
nanoparticles, without aggregation or agglomeration, via
electrostatic forces. Functional inorganic ligands are
inter-particle media, including inorganic complexes, ions, and
molecules that eliminate insulating organic ligands, stabilize the
semiconductor nanoparticles in solution, facilitate close-packing
between semiconductor nanoparticles, and create all-inorganic
colloidal nanostructures that may be processed in solution to form
all-inorganic films.
[0015] After formation of the ink including all-inorganic colloidal
nanostructures, the ink may be deposited using spin-coating,
spray-casting, or inkjet printing techniques on any suitable
substrate conducting or insulating, crystalline or amorphous, rigid
or flexible. Once deposited on the substrate, the all-inorganic
nanostructured ink may be transformed into a solid, all-inorganic
fused film via thermal treatment. The fused film may function as an
optically active layer for optoelectronic devices based on the
fused all-inorganic colloidal nanostructures incorporated into the
fused film. The final material composition, size of the imbedded
all-inorganic colloidal nanostructures, and the thickness of the
fused film may depend on the light or wavelength region selected
for detection.
[0016] According to various embodiment, aspects of the present
disclosure may include an imaging system, a focal plane array which
incorporates a fused film formed that may work as an optically
sensitive layer formed on an underlying integrated circuit
patterned to measure and relay optical signals, electronic signals,
or both, on a pixel-by-pixel basis, where the signal may be
indicative of light absorbed in the medium from which the focal
plane array is made. The circuit may achieve multiplexing of the
values read from individual pixels into row or columns of data,
carried by electrodes and stored for digital imaging. Subsequent
layers, typically processed from the solution phase, which, with
appropriate interfacing, sensitize the underlying focal plane array
to become responsive to the wavelengths absorbed by these new
layers. Their resultant electronic signals may be registered and
relayed using the underlying chip.
[0017] The present disclosure may provide a range of
solution-processed fused films that may lie atop the underlying
chip or active array. In some embodiments, the present disclosure
may provide a method of sensitizing a charge-coupled device (CCD),
complementary metal-oxide-semiconductor (CMOS) focal plane array,
or thin-film transistor (TFT) active pixel array using
all-inorganic fused films.
[0018] Furthermore, the disclosure may provide efficient, highly
sensitive photo detectors based on solution-processed all-inorganic
colloidal nanostructured fused films. Additionally, highly
sensitive photodetectors based on a combination of two (or more)
types of solution-processed all-inorganic colloidal nanostructures,
each including a distinct semiconductor material, are provided.
Multispectral detection of electromagnetic radiation wavelengths or
ranges of wavelengths may be facilitated by incorporating various
sizes of all-inorganic colloidal nanostructures within a single,
continuous optically active layer within the optoelectronic device,
depositing varied respective all-inorganic colloidal nanostructures
per pixel and/or incorporating stacked (e.g., vertical) fused film
layers having a fused all-inorganic colloidal nanostructures, where
each fused film represents an optically active layer in electrical
communication with at least two electrodes.
[0019] In some embodiments, the imaging devices may be efficient
photoconductive optical detectors active in the x-ray, ultraviolet,
visible, short-wavelength infrared, long-wavelength infrared
regions of the spectrum, and are based on solution-processed
nanocrystalline quantum dots. Some embodiments may have the
potential to be used in creating multi-spectral, low-cost, large
area, and flexible-substrate imaging systems.
[0020] In one embodiment, a film comprises fused nanostructures
substantially devoid of organic material wherein the nanostructures
comprise an inorganic nanoparticle fused with a functional
inorganic ligand, and wherein charge carriers are mobile between
the nanostructures and throughout the film.
[0021] In another embodiment, a device, comprises (a) a film
comprising a network of fused all-inorganic nanostructures, wherein
the nanostructures include an inorganic nanoparticle fused with a
functional inorganic ligand, and wherein electrical communication
exists between the nanostructures and throughout the film, and the
film has substantially no defect states in the regions where the
nanostructures are fused; and (b) first and second electrodes in
spaced relation and in electrical communication with first and
second portions of the network of fused nanostructures.
[0022] Additional features and advantages of an embodiment will be
set forth in the description which follows, and in part will be
apparent from the description. The objectives and other advantages
of the invention will be realized and attained by the structure
particularly pointed out in the exemplary embodiments in the
written description and claims hereof as well as the appended
drawings.
[0023] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory and are intended to provide further explanation of
the invention as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Embodiments are described by way of example with reference
to the accompanying figures which are schematic and not intended to
be drawn to scale.
[0025] FIG. 1 is a block diagram of fused film manufacturing
method, according to an embodiment.
[0026] FIG. 2 shows fused film having all-inorganic colloidal
nanostructures on a substrate, according to an embodiment.
[0027] FIG. 3 depicts a fused film with an electrode, according to
an embodiment.
DETAILED DESCRIPTION
[0028] Reference will now be made in detail to the preferred
embodiments, examples of which are illustrated in the accompanying
drawings. The embodiments described above are intended to be
exemplary. One skilled in the art recognizes that numerous
alternative components and embodiments that may be substituted for
the particular examples described herein and still fall within the
scope of the invention.
[0029] The present disclosure is described in detail with reference
to embodiments illustrated in the drawings, which form a part
hereof. In the drawings, which are not necessarily to scale or to
proportion, similar symbols typically identify similar components,
unless context dictates otherwise. Other embodiments may be used
and/or other changes may be made without departing from the spirit
or scope of the present disclosure. The illustrative embodiments
described in the detailed description are not meant to be limiting
of the subject matter presented.
[0030] Definitions
[0031] As used here, the following terms may have the following
definitions:
[0032] "Fused film" refers to a layer of all-inorganic colloidal
semiconductor nanostructures that may be converted into a solid
matrix after a thermal treatment, and which may be optically
active.
[0033] "Optically active" refers to a substance's ability to
convert optical to electrical light.
[0034] "Semiconductor nanoparticles" refers to particles sized
between about 1 and about 100 nanometers made of semiconducting
materials.
[0035] The present disclosure relates to optical devices and
methods of producing devices from films synthesized from
all-inorganic colloidal semiconductor nanostructures. The
all-inorganic colloidal semiconductor nanostructures may be fused
to form nanocrystalline films ("fused films") that may be optically
active and/or photoconductive and may be used in photodiodes,
photodetectors, optical sensors, imaging devices, photovoltaic
applications, among others. Devices incorporating the fused films
may be designed to absorb specific or multiple electromagnetic
wavelengths based on the design of the all-inorganic colloidal
nanostructures having the fused film.
[0036] All-Inorganic Nanostructured Lnks Using Inorganic Functional
Ligands
[0037] FIG. 1 is a block diagram of a fused film manufacturing
method 100.
[0038] In order to produce the ink for the manufacturing of fused
films employed in optoelectronic devices, nanocrystal synthesis 102
may first take place. During nanocrystal synthesis 102,
semiconductor nanoparticles may be produced using known techniques
such as batch or continuous flow wet chemistry processes. The known
synthesis techniques for colloidal nanoparticles may include
capping semiconductor nanoparticle precursors in a stabilizing
organic material, or organic ligands, which may prevent the
agglomeration of the semiconductor nanoparticle during and after
nanocrystal synthesis 102. These organic ligands are long chains
radiating from the surface of the nanoparticle and may assist in
the suspension and/or solubility of the nanoparticle in
solvents.
[0039] Semiconductor nanoparticles employed in the present
disclosure may be spherical nanometer-scale, crystalline materials,
also known as semiconductor nanocrystals or quantum dots. Other
shaped nanometer-scale, crystalline particles may be employed
including oblate and oblique spheroids, rods, wires, and the like.
Semiconductor nanoparticles may include metal, semiconductor,
oxide, metal-oxides and ferromagnetic compositions. The
nanoparticles may have a diameter ranging between about 1 nm and
about 1000 nm, with the preferred range being between about 2 nm
and about 10 nm. Due to the small size of the crystals, quantum
confinement effects may manifest resulting in size, shape, and
compositionally dependent optical and electronic properties, rather
than the properties for the same materials in bulk scale.
[0040] Semiconductor nanoparticles may have a tunable absorption
onset that has increasingly large extinction coefficients at
shorter wavelengths, multiple observable excitonic peaks in the
absorption spectra that correspond to the quantized electron and
hole states, and narrowband tunable band-edge emission spectra.
Semiconductor nanoparticles may absorb light at wavelengths shorter
than the modified absorption onset and emit at the band edge. For
example, using the same materials, the semiconductor nanoparticles
may be manufactured to be optically sensitive to the ultraviolet,
x-ray, visible, and infrared regions of the electromagnetic
spectrum by manufacturing nanoparticles in different sizes.
[0041] Inorganic semiconductor nanoparticles may include II-VI,
III-V, and IV-VI binary semiconductors. Examples of such binary
semiconductor materials may include ZnS, ZnSe, ZnTe, CdS, CdSe,
CdTe, HgS, HgSe, HgTe (II-VI materials), PbS, PbSe, PbTe (IV-VI
materials), AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP,
InAs, and InSb (III-V materials). In addition, the semiconductor
nanoparticles may be ternary, quaternary, and quinary semiconductor
nanostructures and combinations and mixtures of the materials
thereof.
[0042] In some embodiments, the semiconductor nanoparticles may
include core-shell type semiconductors in which the shell is one
type of semiconductor and the core is another type of
semiconductor, metal, oxide, and metal-oxide compounds or
core-shell compositions, and mixtures thereof, which may have
conductive or semi conductive properties or serve to introduce
certain defect states.
[0043] Additionally, fused film manufacturing method 100 may
involve ligand exchange 104, in which substitution of organic
ligands with functional inorganic ligands may be achieved.
Typically, functional inorganic ligands may be dissolved in a polar
solvent, while organic capped semiconductor nanoparticles may be
dissolved in an immiscible, generally non-polar, solvent. These two
solutions may then be combined and stirred for about 10 minutes,
after which a complete transfer of semiconductor nanoparticles from
the non-polar solvent to the polar solvent may be observed.
Immiscible solvents may facilitate a rapid and complete exchange of
organic ligands with functional inorganic ligands.
[0044] Functional inorganic ligands may be soluble functional
reagents that are free from organic functionality, may have a
greater affinity to link to the semiconductor nanoparticles than
the organic ligands, and therefore, may displace the organic
ligands from organic capped semiconductor nanoparticles. Ligand
exchange 104 may involve precipitating the organic capped
semiconductor nanoparticles from their original solution containing
organic ligands, washing, and re-dispersing in a liquid or solvent
which either is or includes the functional inorganic ligands. These
functional inorganic ligands may disassociate the organic ligands
from the outer surfaces of the organic capped semiconductor
nanoparticles and may link the functional inorganic ligands to the
semiconductor nanoparticles. The functional inorganic ligands may
maintain the stability of semiconductor nanoparticles in the
solution and may provide preferred ordering and close-packing of
the semiconductor nanoparticles without aggregation or
agglomeration via electrostatic forces. Functional inorganic
ligands may assist in the suspension and/or solubility of the
semiconductor nanoparticle in solvents or liquids. Once applied,
the functional inorganic ligands may not substantially change the
optoelectronic characteristics of the semiconductor nanoparticles
originally synthesized with organic ligands.
[0045] Functional inorganic ligands may include materials that are
the same as the coordinated semiconductor nanoparticle or different
to design and affect the electronic, optical, magnetic, or other
properties for the final fused films. In some embodiments, two or
more types of semiconductor nanoparticles may be separately
manufactured. Each different type of semiconductor nanoparticle may
be subject to the exchange of organic ligands for functional
inorganic ligands and the extraction of post-exchanged organic
ligands. Subsequently, the two types of semiconductor nanoparticles
with functional inorganic ligands may be mixed in a solution to
create a heterogeneous mixture. A plurality of semiconductor
nanoparticle compositions and/or sizes may be included in the
all-inorganic nanostructured ink. Functional inorganic ligands
fused with semiconductor nanoparticles may have the beneficial
effect of making nanostructured surfaces more stable to oxidation
and photoxidation and increase material performance and
longevity.
[0046] Functional inorganic ligands may include suitable elements
from groups such as polyatomic anions, transition metals,
lanthanides, actinides, chalcogenide molecular compounds, Zintl
ions, inorganic complexes, metal-free inorganic ligands, and/or a
combination including at least one of the foregoing. In some
embodiments, functional inorganic ligands may be partially
volatilized, where some portion of the functional inorganic ligand
remains as solid state electronic material within the
nanostructured ink.
[0047] Examples of polar solvents containing functional inorganic
ligands may include 1,3-butanediol, acetonitrile, ammonia,
benzonitrile, butanol, dimethylacetamide, dimethylamine,
dimethylethylenediamine, dimethylformamide, dimethylsulfoxide
(DMSO), dioxane, ethanol, ethanolamine, ethylenediamine,
ethyleneglycol, formamide (FA), glycerol, methanol, methoxyethanol,
methylamine, methylformamide, methylpyrrolidinone, pyridine,
tetramethylethylenediamine, triethylamine, trimethylamine,
trimethylethylenediamine, water, and mixtures thereof.
[0048] Examples of non-polar or organic solvents containing organic
ligands may include pentane, pentanes, cyclopentane, hexane,
hexanes, cyclohexane, heptane, octane, isooctane, nonane, decane,
dodecane, hexadecane, benzene, 2,2,4-trimethylpentane, toluene,
petroleum ether, ethyl acetate, diisopropyl ether, diethyl ether,
carbon tetrachloride, carbon disulfide, and mixtures thereof;
provided that organic solvent is immiscible with polar solvent.
Other immiscible solvent systems that are applicable may include
aqueous-fluorous, organic-fluorous, and those using ionic
liquids.
[0049] The exchange and extraction of the organic ligands in ligand
exchange 104 may provide a solution or ink of all-inorganic
colloidal nanostructures that may be substantially free of organic
materials. In some embodiments, the relative concentration of the
organic ligands to the semiconductor nanoparticle in the solution
of the functional inorganic ligand may be less than about 10%, 5%,
4%, 3%, 2%, 1%, 0.5% and/or 0.1% of the concentration in a solution
of the semiconductor nanoparticle with the organic ligands.
[0050] Organic materials in organic ligands are known to be less
stable and more susceptible to degradation via oxidation and
photo-oxidation; therefore, all-inorganic materials may enhance the
stability, performance and longevity of the device. In addition,
organic materials may act as insulating agents that prevent the
efficient transport of charge carriers between semiconductor
nanoparticles, resulting in decreased device efficiencies.
[0051] Semiconductor nanoparticles with inorganic functional
ligands may differ from core/shell nanoparticles where one
nanoparticle has an outer crystalline layer with a different
chemical formula. The crystalline layer, or shell, generally forms
over the entire semiconductor nanoparticle but, as used in the
present disclosure, core/shell nanoparticles may refer to those
nanoparticles where at least one surface of the semiconductor
nanoparticle is coated with a crystalline layer. While the
functional inorganic ligands may form ordered arrays that may
radiate from the surface of a semiconductor nanoparticle, these
arrays may differ from a core/shell crystalline layer, as they are
not permanently bound to the core semiconductor nanoparticle in the
all-inorganic nanostructured ink.
[0052] After ligand exchange 104, which may form an all-inorganic
nanostructured ink, the ink may undergo a deposition 106 over a
substrate or may be deposited as additional layers to all-inorganic
fused films. Deposition 106 techniques may include: blading,
growing three-dimensional ordered arrays, spin coating, spray
coating, spray pyrolysis, dipping/dip-coating, sputtering,
printing, inkjet printing, stamping, the like and combinations
thereof.
[0053] Following deposition 106, all-inorganic nanostructured ink
may be transformed into a solid, all-inorganic fused film via
thermal treatment 108. Crystalline films from all-inorganic
colloidal nanostructures may be formed by a low temperature thermal
treatment 108. In at least one embodiment, thermal treatment 108 of
the colloidal material may include heating to a temperature less
than about 350, 300, 250, 200, 150, 100 and/or 80.degree. C. Fused
film 200 may maintain approximately the same optoelectronic
characteristics as the all-inorganic nanostructured ink or solution
including the all-inorganic colloidal nanostructures. This may
require that the fused film substantially maintains the same size
and shape of the semiconductor nanoparticles that were deposited
from the all-inorganic nanostructured ink. Excessive thermal
treatment 108 may create fused films that do not maintain
nanostructures and may result in fused films that have
optoelectronic characteristics more closely performing to the
respective bulk semiconductor material. Deposition 106 of
all-inorganic nanostructured inks and film fusing via thermal
treatment 108 to create all-inorganic nanostructured films may be
performed in repetition to achieve desired film characteristics,
including multiple layers, for use in optoelectronic devices.
[0054] Continuous Inorganic Fused Films from Inks Having
All-Inorganic
[0055] Nanostructures
[0056] FIG. 2 shows fused film 200. Fused film 200 may be enhanced
as an optically active layer for finished optoelectronic devices
based on fused all-inorganic colloidal nanostructures 204
integrated into fused film 200. Final material composition, size of
imbedded all-inorganic colloidal nanostructures 204, and thickness
of fused film 200 may be dependent on light or wavelength region
selected for detection. Thickness of fused film 200 may range
between about 50 nm and about 3 um, though thinner or thicker fused
films 200 may be employed according to the desired functionality of
the device.
[0057] The functional inorganic ligands may effectively bridge the
semiconductor nanoparticles to form an electrical network and
facilitate efficient electronic transport between all-inorganic
colloidal nanostructures 204 within fused film 200. The fused
all-inorganic colloidal nanostructures 204, and the juncture
between them, may generally not have defect states, so current will
flow readily between them. This aspect of fusing all-inorganic
colloidal nanostructures 204, including functional inorganic
ligands, may increase the electronic transport properties between
all-inorganic colloidal nanostructures 204 and throughout fused
film 200, providing a carrier mobility which may range within about
0.01 cm.sup.2/Vs and about 80 cm.sup.2/Vs. Fused film 200 having
all-inorganic colloidal nanostructures 204 may also exhibit a
relatively low electrical resistance above about 25
k-Ohm/square.
[0058] Nanostructured ligands remaining in the deposited
all-inorganic ink/solution to form fused film 200 may not be
removed, either before or as a function of the fusing steps or
thermal treatment. Furthermore, inks including all-inorganic
colloidal nanostructures 204 may lose less than about 20%, 15%, 10%
and/or 5% of their mass upon a thermal treatment up to about
400.degree. C. and/or 450.degree. C.
[0059] Optical Devices With Optically Active Layers Having
All-Inorganic Nanostructured Fused Films
[0060] FIG. 3 depicts a fused film structure 300. Optical devices
may include single image sensor chips having a plurality of
pixelated metal oxide semiconductors each of which may include
fused film 200 that may be optically active and at least two
electrodes 302 in electrical communication with fused film 200.
Size of pixels may range from less than about 1 micron square to
about 1 micron square.
[0061] Other optical devices may be large-area image sensors
including active pixel or matrix arrays incorporating thin film
transistors (TFTs) which may include fused film 200 that is
optically active and at least two electrodes 302 in electrical
communication with fused film 200. Pixel size may be reduced to
about 40 microns square or may be sized to accommodate the detected
wavelength as required.
[0062] Current and/or voltage between electrodes 302 may be related
to the amount of light absorbed by fused film 200. Photons absorbed
by fused film 200 may generate electron-hole pairs and a current
and/or voltage. By determining such current and/or voltage for each
pixel, the image across the chip may be reconstructed via digital
multiplexing and other integrated circuit components. The
responsiveness of the sensor chips to different electromagnetic
wavelengths may be made tunable by changing the material systems
for the all-inorganic colloidal nanostructures 204 inks and/or
changing the size of the all-inorganic colloidal nanostructures 204
within fused film 200 to take advantage of the quantum size effects
in all-inorganic colloidal nanostructures 204 included in the
ink.
[0063] Fused film 200 may be deposited and created as a monolithic
layer(s) over the image sensor chip, integrated circuit, integrated
circuit components, and/or TFT active matrices. Fused film 200 may
be solution-deposited onto a substrate 202 or pre-fabricated CCD,
CMOS, or TFT electronics.
[0064] Image sensor chip, integrated circuit, and/or TFT
architecture may include one or more semiconducting materials, such
as silicon, silicon-on-insulator, silicon-germanium, indium
phosphide, indium gallium arsenide, gallium arsenide, or
semiconducting polymers (for flexible substrate and non-planar
devices). Optical device substrates 202 may also include plastic
and glass. In addition, flexible substrate 202 devices may include
metal foil and organic substrates.
[0065] Additional layers may be included in the layers atop the
structure, including additional depositions of all-inorganic
colloidal nanostructures 204 on fused film 200 to enable
multispectral detection and subsequent layers of at least partially
transparent electrodes. Multiple optically active layers may be
layered on the image sensor substrate 202 to provide greater
sensitivity for the respective wavelengths, improved imaging for
multiple wavelengths, decreased complexity in device architectures
(e.g., multilayer, monolithic deposition and without additional
color or wavelength filters). Moreover, additional optically active
layers may include additional contact electrodes per layer.
[0066] Contact electrodes 302 may be at least partially transparent
and overlay all-inorganic colloidal nanostructures 204 in fused
film 200. Electrode 302 materials may include aluminum, gold,
platinum, silver, magnesium, copper, indium tin oxide (ITO), tin
oxide, tungsten oxide, layer structures and combinations
thereof.
[0067] Substrates 202 may include one or more electrodes 302, or
electrodes 302 may be deposited in a later step. Optical devices
may also be large-area image sensors on plastic or other flexible
substrates.
[0068] The embodiments described above are intended to be
exemplary. One skilled in the art recognizes that numerous
alternative components and embodiments that may be substituted for
the particular examples described herein and still fall within the
scope of the invention.
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