U.S. patent application number 17/034152 was filed with the patent office on 2021-01-14 for quantum dot led with spacer particles.
This patent application is currently assigned to Nanosys, Inc.. The applicant listed for this patent is Nanosys, Inc.. Invention is credited to Charles HOTZ, Christian IPPEN, Jesse MANDERS, Jonathan TRUSKIER, Donald ZEHNDER.
Application Number | 20210013371 17/034152 |
Document ID | / |
Family ID | 1000005109672 |
Filed Date | 2021-01-14 |
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United States Patent
Application |
20210013371 |
Kind Code |
A1 |
MANDERS; Jesse ; et
al. |
January 14, 2021 |
QUANTUM DOT LED WITH SPACER PARTICLES
Abstract
Embodiments of the present application relate to the use of
quantum dots mixed with spacer particles. An illumination device
includes a first conductive layer, a second conductive layer, and
an active layer disposed between the first conductive layer and the
second conductive layer. The active layer includes a plurality of
quantum dots that emit light when an electric field is generated
between the first and second conductive layers. The quantum dots
are interspersed with spacer particles that do not emit light when
the electric field is generated between the first and second
conductive layers.
Inventors: |
MANDERS; Jesse; (Mountain
View, CA) ; IPPEN; Christian; (Sunnyvale, CA)
; ZEHNDER; Donald; (San Carlos, CA) ; TRUSKIER;
Jonathan; (Oakland, CA) ; HOTZ; Charles; (San
Rafael, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nanosys, Inc. |
Milpitas |
CA |
US |
|
|
Assignee: |
Nanosys, Inc.
Milpitas
CA
|
Family ID: |
1000005109672 |
Appl. No.: |
17/034152 |
Filed: |
September 28, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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15824701 |
Nov 28, 2017 |
10790411 |
|
|
17034152 |
|
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62428888 |
Dec 1, 2016 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 33/06 20130101;
H01L 33/08 20130101; H01L 33/42 20130101; H01L 33/0029 20130101;
H01L 51/502 20130101; H01L 33/14 20130101; H01L 33/0083
20130101 |
International
Class: |
H01L 33/06 20060101
H01L033/06; H01L 51/50 20060101 H01L051/50; H01L 33/00 20060101
H01L033/00; H01L 33/14 20060101 H01L033/14 |
Claims
1. A method of making an illumination device, comprising:
depositing a first conductive layer on a substrate; mixing a
plurality of quantum dots with a plurality of spacer particles to
form an active mixture, wherein the plurality of spacer particles
comprises a first group of spacer particles and a second group of
spacer particles, and wherein the first group of the spacer
particles has a first spacer particle size substantially equal to a
size of the quantum dots and the second group of the spacer
particles has a second spacer particle size smaller than the size
of the quantum dots; depositing the active mixture as an active
layer located above the first conductive layer, wherein the active
layer comprises the quantum dots interspersed with the spacer
particles; and depositing a second conductive layer above the
active layer, wherein the quantum dots are configured to emit light
when an electric field is generated between the first and second
conductive layers, and the spacer particles are configured to not
emit light when the electric field is generated between the first
and second conductive layers.
2. The method of claim 1, wherein the depositing the active mixture
comprises spin-coating the active mixture to form the active
layer.
3. The method of claim 1, wherein the mixing comprises mixing the
plurality of quantum dots with the plurality of spacer particles in
a solvent.
4. The method of claim 3, further comprising releasing the solvent
from the active layer at room temperature.
5. The method of claim 1, further comprising forming the quantum
dots to each comprise a core structure and a shell structure
surrounding the core structure.
6. The method of claim 5, wherein the spacer particles comprise the
same material as the shell structure.
7. The method of claim 5, further comprising binding ligands to the
shell structure of the quantum dots.
8. The method of claim 7, further comprising binding ligands to the
spacer particles.
9. The method of claim 7, wherein the ligands on the quantum dots
are the same as the ligands on the spacer particles.
10. The method of claim 1, further comprising: depositing a first
transport layer on the first conductive layer, the first transport
layer being configured to facilitate the transport of holes from
the first conductive layer to the active layer; and depositing a
second transport layer on the active layer, the second transport
layer configured to facilitate the transport of electrons from the
second conductive layer to the active layer.
11. A method of fabricating a quantum dot light emitting diode
(QLED), comprising: depositing a first electrode on a substrate;
forming a mixture of quantum dots and spacer particles, wherein the
spacer particles comprise a first group of spacer particles and a
second group of spacer particles, and wherein the first group of
the spacer particles has a first spacer particle size substantially
equal to a size of the quantum dots and the second group of the
spacer particles has a second spacer particle size smaller than the
size of the quantum dots; depositing the mixture to form an active
layer on the first electrode, wherein the active layer comprises
the quantum dots interspersed with the spacer particles; and
depositing a second electrode on the active layer.
12. The method of claim 11, wherein the depositing the mixture
comprises spin-coating the mixture to form the active layer.
13. The method of claim 11, wherein the mixing comprises mixing the
quantum dots and the spacer particles in a non-polar solvent.
14. The method of claim 11, wherein the mixing comprises mixing the
quantum dots and the spacer particles in a 1:1 concentration ratio
by weight, in a 1:2 concentration ratio by weight, or in a 2:1
concentration ratio by weight.
15. The method of claim 11, further comprising forming the quantum
dots to each comprise a core structure and a shell structure
surrounding the core structure.
16. The method of claim 11, wherein the spacer particles comprise a
same material as the quantum dots.
17. The method of claim 11, further comprising: forming the quantum
dots to each comprise a core structure and a shell structure
surrounding the core structure; and binding ligands to the shell
structure of the quantum dots.
18. The method of claim 11, further comprising binding ligands to
the spacer particles.
19. The method of claim 11, further comprising depositing a
semiconductor polymer layer between the first electrode and the
active layer.
20. The method of claim 11, further comprising: depositing a first
transport layer on the first electrode, the first transport layer
being configured to facilitate the transport of holes from the
first electrode to the active layer; and depositing a second
transport layer on the active layer, the second transport layer
configured to facilitate the transport of electrons from the second
electrode to the active layer.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 15/824,701, filed Nov. 28, 2017, which claims the benefit
of U.S. Provisional Application No. 62/428,888, filed Dec. 1, 2016.
The disclosures of both applications are incorporated by reference
in their entireties.
FIELD
[0002] The present application relates to quantum dot emission
technology, and to illumination devices that include a mixture of
quantum dots and spacer particles.
BACKGROUND
[0003] Semiconductor nanocrystallites (quantum dots) whose radii
are smaller than the bulk exciton Bohr radius constitute a class of
materials intermediate between molecular and bulk forms of matter.
Quantum confinement of both the electron and hole in all three
dimensions leads to an increase in the effective band gap of the
material with decreasing crystallite size. Consequently, both the
optical absorption and emission of quantum dots shift to the blue
(higher energies) as the size of the dots gets smaller. Quantum
dots can absorb light having a first wavelength and emit light
having a longer wavelength than that absorbed. Incorporating
quantum dots in display devices, such as LCDs, has been shown to
produce highly vibrant colors while reducing the overall power
consumption. Quantum dots provide desirable characteristics due to
their low power consumption, low manufacturing cost, and highly
vibrant light output.
[0004] A quantum dot LED (QLED) generally consists of a multilayer
structure wherein successive layers are deposited on top of each
other in sequential order. A general QLED structure includes an
active layer consisting of quantum dots (QDs). It has been shown
that when QDs are in close proximity to each other, non-radiative
quenching pathways such as Forster resonance energy transfer, are
active. This effectively reduces the QDs' light-emitting
efficiency.
SUMMARY
[0005] Embodiments of the present application relate to a technique
for mitigating the non-radiative quenching that occurs when QDs are
in close proximity to one another.
[0006] According to an embodiment, an illumination device includes
a first conductive layer, a second conductive layer, and an active
layer disposed between the first conductive layer and the second
conductive layer. The active layer includes a plurality of quantum
dots that emit light when an electric field is generated between
the first and second conductive layers. The quantum dots are
interspersed with spacer particles that do not emit light when the
electric field is generated between the first and second conductive
layers.
[0007] According to another embodiment, a method of making an
illumination device includes depositing a first conductive layer on
a substrate. The method also includes mixing a plurality of quantum
dots with a plurality of spacer particles to form an active mixture
and depositing the active mixture as an active layer located above
the first conductive layer. The active layer includes the quantum
dots interspersed with the spacer particles. The method also
includes depositing a second conductive layer above the active
layer. The quantum dots in the active layer emit light when an
electric field is generated between the first and second conductive
layers while the spacer particles do not emit light when the
electric field is generated between the first and second conductive
layers.
[0008] Further features and advantages of the invention, as well as
the structure and operation of various embodiments of the
invention, are described in detail below with reference to the
accompanying drawings. It is noted that the invention is not
limited to the specific embodiments described herein. Such
embodiments are presented herein for illustrative purposes only.
Additional embodiments will be apparent to persons skilled in the
relevant art(s) based on the teachings contained herein.
BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES
[0009] The accompanying drawings, which are incorporated herein and
form part of the specification, illustrate the present embodiments
and, together with the description, further serve to explain the
principles of the present embodiments and to enable a person
skilled in the relevant art(s) to make and use the present
embodiments.
[0010] FIG. 1 illustrates the structure of a quantum dot (QD),
according to an embodiment.
[0011] FIG. 2 illustrates a view of QDs interspersed with spacer
particles, according to an embodiment.
[0012] FIG. 3 illustrates a layer structure of an illumination
device, according to an embodiment.
[0013] FIG. 4 illustrates a flowchart of an example method of
making an illumination device.
[0014] The features and advantages of the present embodiments will
become more apparent from the detailed description set forth below
when taken in conjunction with the drawings, in which like
reference characters identify corresponding elements throughout. In
the drawings, like reference numbers generally indicate identical,
functionally similar, and/or structurally similar elements. The
drawing in which an element first appears is indicated by the
leftmost digit(s) in the corresponding reference number.
DETAILED DESCRIPTION OF THE INVENTION
[0015] Although specific configurations and arrangements may be
discussed, it should be understood that this is done for
illustrative purposes only. A person skilled in the pertinent art
will recognize that other configurations and arrangements can be
used without departing from the spirit and scope of the present
invention. It will be apparent to a person skilled in the pertinent
art that this invention can also be employed in a variety of other
applications beyond those specifically mentioned herein.
[0016] It is noted that references in the specification to "one
embodiment," "an embodiment," "an example embodiment," etc.,
indicate that the embodiment described may include a particular
feature, structure, or characteristic, but every embodiment may not
necessarily include the particular feature, structure, or
characteristic. Moreover, such phrases do not necessarily refer to
the same embodiment. Further, when a particular feature, structure
or characteristic is described in connection with an embodiment, it
would be within the knowledge of one skilled in the art to effect
such feature, structure or characteristic in connection with other
embodiments whether or not explicitly described.
[0017] It should be understood that the words "above" and "below"
are used herein to identify relative position of one layer to
another, and that there may be intervening layers between the two.
For example, if a first layer is said to be above a second layer,
then the first layer may be directly on the second layer, or there
may be other layers between the first layer and second layer.
Conversely, it should be understood that the word "on" is used
herein to identify that a layer is directly contacting another
layer. For example, if a first layer is said to be on a second
layer, then the first layer is in direct contact with the second
layer. It should also be understood that the word "between" is used
herein to identify a position of a layer relative to two other
layers, even though there can be intervening layers. For example,
if a first layer is said to be between a second layer and a third
layer, then the first layer may contact both the second and third
layers, or there may be intervening layers between the first layer
and the second layer and between the first layer and the third
layer.
[0018] Before describing the details of the embodiments herein, a
brief description of quantum dots (QDs) will be discussed. Quantum
dots may be used in a variety of applications that benefit from
having sharp, stable, and controllable emissions in the visible and
infrared spectrum. FIG. 1 illustrates an example of the core-shell
structure of a quantum dot 100, according to an embodiment. Quantum
dot 100 includes a core material 102, an optional buffer layer 104,
a shell material 106, and a plurality of ligands 108.
[0019] Core material 102 includes a semiconducting material that
emits light upon absorption of higher energies. Examples of core
material 102 include indium phosphide (InP), cadmium selenide
(CdSe), zinc sulfide (ZnS), zinc selenide (ZnSe), lead sulfide
(PbS), indium arsenide (InAs), indium gallium phosphide, (InGaP),
and cadmium telluride (CdTe). Any other III-V, tertiary, or
quaternary semiconductor structures that exhibit a direct band gap
may be used as well. Of these materials, InP and CdSe are most
often used, but InP is more desirable to implement over CdSe due to
the toxicity of CdSe dust. Additionally, ZnSe has been used to form
blue-emitting QDs. ZnSe may exhibit emissions having a
full-width-half-max (FWHM) of between about 10 nm and about 20 nm.
CdSe may exhibit emissions having a FWHM range of around 30 nm,
while InP may exhibit emissions having a FWHM range of around 40
nm.
[0020] Buffer layer 104 may surround core material 102. Buffer
layer 104 may be zinc selenide sulfide (ZnSeS) and is typically
very thin (e.g., on the order of 1 monolayer). Buffer layer 104 may
have a wider band gap than core material 102, thus confining
excitation to the core of quantum dot 100. Buffer layer 104 may
have a lattice constant between that of core material 102 and shell
material 106 to result in a smooth interface between core material
102 and shell material 106, therefore increasing the quantum
efficiency.
[0021] Shell material 106 may be on the order of two monolayers
thick and is typically, though not required, also a semiconducting
material. The shells provide protection to core material 102. A
commonly used shell material is zinc sulfide (ZnS), although other
materials may be used as well. Shell material 106 may be formed via
a colloidal process similar to that used to form core material
102.
[0022] In another embodiment, quantum dot 100 does not have
distinct core and shell regions, but rather a material gradient
from the center of quantum dot 100 moving outwards to the edge of
quantum dot 100.
[0023] Ligands 108 may be adsorbed or bound to an outer surface of
shell material 106. Ligands 108 may be included to help separate
(e.g., disperse) the quantum dots from one another. If the quantum
dots are allowed to aggregate as they are being formed, the quantum
efficiency drops and quenching of the optical emission occurs.
Ligands 108 may also be used to impart certain properties to
quantum dot 102, such as hydrophobicity, or to provide reaction
sites for other compounds to bind. A wide variety of ligands 108
exist that may be used with quantum dot 102. In an embodiment,
ligands 108 from the aliphatic amine or aliphatic acid families are
used. Further details on the fabrication of the quantum dots may be
found in U.S. Pat. Nos. 9,169,435, 9,199,842, and 9,139,770, the
discloses of which are each incorporated herein by reference.
[0024] The use of ligands 108 on the QDs may not be enough to
satisfactorily reduce quenching. QDs may still aggregate too
closely resulting in the activation of non-radiative quenching
pathways such as Forster resonance energy transfer. According to an
embodiment, QDs are further spaced from one another by mixing with
non-luminescent spacer particles.
[0025] FIG. 2 illustrates an example mixture of QDs 100 with spacer
particles 202 in a solvent solution, according to an embodiment.
Spacer particles 202 may be synthesized separately from QDs 100 and
then mixed with QDs any time during or after the synthesis of QDs
and before the solution is deposited to form an active layer of the
QDs in a device. The solvent solution may include any non-polar
solvent such as toluene, hexane, heptane, octane, nonane, decane,
cyclohexane, p-/o-/m-xylene, mesitylene, chloroform, chlorobenzene,
or p-/o-/m-dichlorobenzene to name a few examples. Polar solvents
may be possible to use as well if ligands 108 are non-aliphatic
and/or exhibit a hydrophilic moiety interacting with the polar
solvent.
[0026] Spacer particles 202 may comprise any inorganic particles,
according to an embodiment. Ideally, spacer particles 202 should
not emit any light during activation of QDs 100. In one example,
spacer particles 202 should have a bandgap that is at least wider
than that of QDs 100. In another example, spacer particles 202
should not be too insulative such that they act as a charge
injection barrier between QDs 100 and the neighboring hole or
electron transport layers in a device. According to an embodiment,
spacer particles 202 comprise a semiconducting material. In one
example, spacer particles 202 are the same material as the shell
structure of QDs 100. If QDs 100 have a blue-emitting ZnSe core
with a ZnS shell, then spacer particles 202 may also be ZnS, for
example. Spacer particles 202 may all be the same material, or may
be various materials.
[0027] Spacer particles 202 may include ligands (not shown) bound
to an outer surface of spacer particles 202 to prevent aggregate
clumping of the particles, according to an embodiment. In one
example, the ligands on spacer particles 202 are the same as
ligands 108 on QDs 100.
[0028] Spacer particles 202 may vary in size, shape, and
concentration. Spacer particles 202 may be about the same size, on
average, as QDs 100. Differently sized spacer particles 202 may be
mixed with QDs 100 to affect the spacing and charge transport
ability of the QDs 100. For example, QDs 100 may be mixed with a
first concentration of spacer particles that have about the same
size as QDs 100, and with a second concentration of spacer
particles that have smaller size than QDs 100. In an embodiment,
spacer particles 202 may be mixed with QDs 100 in a 2:1
concentration ratio by weight. In another embodiment, spacer
particles 202 may be mixed with QDs 100 in a 1:1 concentration
ratio by weight. In yet another embodiment, spacer particles 202
may be mixed with QDs 100 in a 1:2 concentration ratio by
weight.
[0029] Table 1 below provides quantum yield and absorbance data for
various mixtures of QDs and spacer particles deposited over a layer
of polyvinyl carbazole (PVK). The QDs were blue-emitting ZnSe/ZnS,
while the spacer particles were ZnS particles having an average
size of 9 nm with an absorption onset of 355 nm. Such spacer
particles were found to be suitable for mixing with the QDs due to
their similar particle size, wider band gap, and identical surface
ligands to help ensure miscibility.
TABLE-US-00001 TABLE 1 Film Sample Quantum Yield Absorbance (OD)
PVK/QD only 21.5% 0.040 PVK/(ZnS + QD 2:1) 65.6% 0.013 PVK/(ZnS +
QD 1:1) 76.6% 0.022 PVK/(ZnS + QD 1:2) 53.8% 0.016
[0030] As can be seen from the data in Table 1, the quantum yield
of the film sample substantially increases when using the ZnS
spacer particles versus no spacer particles. The quantum yield was
at its highest when the concentration by weight of the spacer
particles to the QDs was even. The quantum yield decreased when the
concentration by weight of QDs was larger than the concentration of
spacer particles, likely due to the quenching that occurs when the
QDs are too close to one another. Similarly, the sample that
includes only QDs exhibited the lowest quantum yield. The
absorbance data indicates that the total concentration of QDs was
much lower in the samples that included a mixture with spacer
particles versus the sample with only QDs, yet the quantum yield
was higher in these samples with the lower QD concentration.
[0031] FIG. 3 illustrates an example layer structure that may be
used in an illumination device, according to an embodiment. The
illumination device may be a quantum dot light emitting diode
(QLED). The illumination device may be used in a wide variety of
applications, such as flexible electronics, touchscreens, monitors,
televisions, cellphones, and any other high definition displays.
Other layers may be included in the layer structure beyond those
specifically illustrated in FIG. 3.
[0032] The layer structure of the illumination device includes a
substrate 302. Substrate 302 may be a transparent substrate, such
as glass. Substrate 302 may be a flexible material such as
polyimide, or a flexible and transparent material such as
polyethylene terephthalate. Substrate 302 may have a thickness of
about 0.1 mm to 2 mm. Disposed on the glass substrate 302 is a
first conductive layer 304. According to an embodiment, first
conductive layer 304 comprises indium tin oxide (ITO), which is a
substantially transparent conductive material. First conductive
layer 304 may represent a stack of conductive layers. For example,
first conductive layer 304 may include a layer of ITO and a layer
of aluminum. First conductive layer 304 may have a thickness
between about 50 nm and about 250 nm. First conductive layer 304
may be deposited as a thin film using any known deposition
technique, such as, for example, sputtering or electron-beam
evaporation.
[0033] The total layer structure may be sandwiched between first
conductive layer 304 and a second conductive layer 306, according
to an embodiment. First conductive layer 304 may act as the anode
of the device while second conductive layer 306 acts as the cathode
of the device. Second conductive layer 306 may be a metal, such as
aluminum, and has a thickness between about 100 nm and about 150
nm, according to an embodiment. Similar to first conductive layer
304 described above, second conductive layer 306 may represent a
stack of conductive layers. For example, second conductive layer
304 may include a layer of silver sandwiched between two layers of
ITO (ITO/Ag/ITO). When a potential is applied across first
conductive layer 304 and second conductive layer 306, an electric
field is generated between the two conductive layers, and the
transport of holes and electrons occurs.
[0034] The layer structure may also include a semiconductor polymer
layer 308. Including semiconductor polymer layer 308 is optional,
but the layer may be useful for hole injection. An example polymer
for semiconductor polymer layer 308 is
poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS).
Semiconductor polymer layer 308 may have a thickness between about
20 nm and about 60 nm.
[0035] The layer structure may include transport layers to
facilitate the transport of electrons and holes affected by the
generated electric field between first conductive layer 304 and
second conductive layer 306. A first transport layer 310 associated
with first conductive layer 304 may be included, while a second
transport layer 312 associated with second conductive layer 306 may
be included. First transport layer 310 may act as a hole transport
layer (and an electron and/or exciton blocking layer) when first
conductive layer 304 acts as an anode (i.e., positively charged).
First transport layer 310 may include copper oxide (Cu2O) and
copper gallium oxide nanoparticles (Cu.sub.xGa.sub.1-xO). First
transport layer 310 may also comprise an organic material such as
N,N'-Di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine
(NPB),
Poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl)
diphenylamine)] (TFB), or Poly(9-vinylcarbazole) (PVK) to name a
few examples.
[0036] Second transport layer 312 may act as an electron transport
layer (and a hole and/or exciton blocking layer) when second
conductive layer 306 acts as a cathode (i.e., negatively charged).
Second transport layer 312 may include zinc oxide (ZnO) or zinc
magnesium oxide nanoparticles (Zn.sub.xMg.sub.1-xO). Second
transport layer 312 may also comprise an organic material such as
Tris(2,4,6-trimethyl-3-(pyridin-3-yl)phenyl)borane (3TPYMB) or
2,2',2''-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole)
(TPBi) to name a few examples.
[0037] The roles of first transport layer 310 and second transport
layer 312 are reversed when the polarity of first conductive layer
304 and second conductive layer 306 are reversed. First transport
layer 310 and second transport layer 312 may each have a thickness
between about 20 nm and about 50 nm. Each of first transport layer
310 and second transport layer 312 may be substantially transparent
to visible light.
[0038] Sandwiched between first transport layer 310 and second
transport layer 312 is an active layer 314 that includes a
plurality of QDs interspersed with a plurality of spacer particles,
according to an embodiment. Active layer 314 may be formed by
depositing the mixture of QDs 100 and spacer particles 202 followed
by allowing the solvent to evaporate. In one example, the solvent
evaporates at room temperature. In other example, heat is applied
to the deposited film to hasten the evaporation of the solvent. The
mixture of QDs 100 and spacer particles 202 may be deposited using
a spin-coating technique as would be understood to a person skilled
in the relevant art. Other manufacturing methods may be used.
Active layer 314 may have a thickness between about 10 nm and about
50 nm.
[0039] When an electric field is applied between first conductive
layer 304 and second conductive layer 306, the QDs within active
layer 314 will emit light. The wavelengths of the emitted light
will depend on the size and/or composition of the QD particles
within active layer 314. Active layer 314 may include various-sized
QDs to emit light across a range of wavelengths in the visible
and/or infrared portion of the spectrum. The spacer particles
present in active layer 314 are designed such that they do not emit
light when the electric field is applied between first conductive
layer 304 and second conductive layer 306, according to an
embodiment. The spacer particles may also have a band gap large
enough such that the spacer particles do not absorb the light
emitted by the QDs.
[0040] It should be noted that although the embodiments disclosed
herein relate to a QLED structure where an electric field is
applied to cause the QDs to emit light, other applications with QDs
may also benefit from the physical separation of the QDs using
spacer particles. For example, a layer of QDs may be subjected to
excitation light that is absorbed by the QDs and causes the QDs to
emit light having a longer wavelength than the excitation light.
Such QDs may also be physically separated using spacer particles,
thus enhancing the brightness of the emitted light. In this
example, a blue light source may be used to provide the excitation
light to QDs that emit red and green light when absorbing the blue
light.
[0041] FIG. 4 illustrates a flowchart of an example method 400 for
making an illumination device, according to an embodiment. Some
steps have been omitted to focus discussion on those that are more
relevant. It should also be understood that the steps of method 400
may be performed in a different order without deviating from the
scope or spirit of the invention.
[0042] Method 400 begins with block 402 where a first conductive
layer is deposited. The first conductive layer may be deposited on
a transparent substrate. In one embodiment, the first conductive
layer is ITO.
[0043] Method 400 continues with block 404 where QDs are mixed with
spacer particles, according to an embodiment. The QDs may be mixed
with the spacer particles in a solvent. The concentration ratio by
weight of QDs to spacer particles may be 1:2, 2:1, or 1:1, to name
a few examples.
[0044] Method 400 continues with block 406 where the solvent
mixture of QDs and spacer particles is deposited to form an active
layer, according to an embodiment. The mixture is deposited above
the first conductive layer, although it need not be deposited
directly on the first conductive layer. The mixture may be
deposited by spin-coating the solvent to a final thickness of
around 30 nm. Following deposition, the solvent may be evaporated
at room temperature to leave behind the QDs and spacer particles in
the active layer.
[0045] Method 400 continues with block 408 where a second
conductive layer is deposited above the active layer. The second
conductive layer may be a metal, such as aluminum. The first and
second conductive layers may act as the anode and cathode,
respectively, of the illumination device.
[0046] Method 400 may include other steps related to the synthesis
of the QDs and spacer particles. These synthesis steps may involve
the formation of the core/shell structure of the QDs and binding
ligands to the outer surface of the QDs and the spacer particles.
Method 400 may also include steps for depositing a first transport
layer on the first conductive layer, and depositing a second
transport layer on the active layer. The first transport layer
facilitates the transport of holes from the first conductive layer
to the active layer and the second transport layer facilitates the
transport of electrons from the second conductive layer to the
active layer.
[0047] It is to be appreciated that the Detailed Description
section, and not the Summary and Abstract sections, is intended to
be used to interpret the claims. The Summary and Abstract sections
may set forth one or more but not all exemplary embodiments of the
present invention as contemplated by the inventor(s), and thus, are
not intended to limit the present invention and the appended claims
in any way.
[0048] The present invention has been described above with the aid
of functional building blocks illustrating the implementation of
specified functions and relationships thereof. The boundaries of
these functional building blocks have been arbitrarily defined
herein for the convenience of the description. Alternate boundaries
can be defined so long as the specified functions and relationships
thereof are appropriately performed.
[0049] The foregoing description of the specific embodiments will
so fully reveal the general nature of the invention that others
can, by applying knowledge within the skill of the art, readily
modify and/or adapt for various applications such specific
embodiments, without undue experimentation, without departing from
the general concept of the present invention. Therefore, such
adaptations and modifications are intended to be within the meaning
and range of equivalents of the disclosed embodiments, based on the
teaching and guidance presented herein. It is to be understood that
the phraseology or terminology herein is for the purpose of
description and not of limitation, such that the terminology or
phraseology of the present specification is to be interpreted by
the skilled artisan in light of the teachings and guidance.
[0050] The breadth and scope of the present invention should not be
limited by any of the above-described exemplary embodiments, but
should be defined only in accordance with the following claims and
their equivalents.
* * * * *