阅读说明：本技术 使用量子点增加微型led设备的光输出的方法 (Method for increasing light output of micro LED device using quantum dots ) 是由 E·C·李 于 2018-03-27 设计创作，主要内容包括：描述了基于量子点技术的照明设备及其制造方法。一种照明设备,其包括具有多个微型LED的基材、分束器和具有多个量子点的膜。所述分束器包括多个层,并且设置在所述基材和所述具有多个量子点的膜之间。(A lighting device based on quantum dot technology and a method of manufacturing the same are described. An illumination device includes a substrate having a plurality of micro-LEDs, a beam splitter, and a film having a plurality of quantum dots. The beam splitter includes a plurality of layers and is disposed between the substrate and the film having the plurality of quantum dots.)

1. An illumination apparatus, comprising:

A substrate comprising a plurality of micro-LEDs;

A film comprising a plurality of quantum dots; and

A beam splitter comprising a plurality of layers, wherein the beam splitter is disposed between the substrate and the film.

2. the lighting device of claim 1, wherein each of the plurality of micro-LEDs is configured to emit light only in a blue wavelength range.

3. The lighting device according to any one of the preceding claims, wherein the substrate is a flexible substrate.

4. The lighting device according to any one of the preceding claims, wherein the plurality of layers are arranged such that the beam splitter transmits at least 90% of light having a wavelength between 400nm and 480nm and reflects at least 90% of light having a wavelength between 500nm and 800 nm.

5. The lighting device according to any one of the preceding claims, wherein the plurality of layers comprises titanium dioxide, tantalum pentoxide or silicon dioxide.

6. the lighting device of any one of the preceding claims, wherein the substrate is a surface area of less than 750cm²A die of (a).

7. The lighting device according to any one of the preceding claims, wherein the plurality of quantum dots comprises quantum dots configured to emit light in a green wavelength range, and quantum dots configured to emit light in a red wavelength range.

8. The lighting device according to any one of the preceding claims, wherein the beam splitter comprises a composite laminate structure comprising a plurality of layers.

9. The illumination device according to any one of claims 1 to 7, wherein the thickness of the beam splitter is between 1 μm and 50 μm.

10. The illumination device of any one of claims 1 to 7, wherein the beam splitter comprises a plurality of stacked film layers formed from extruded polymer.

11. the lighting device according to any one of the preceding claims, wherein the film comprises a first layer, a second layer and an adhesive material disposed between the first layer and the second layer, the adhesive material comprising quantum dots.

12. A method of manufacturing a lighting device, the method comprising:

Forming a plurality of micro-LEDs on a substrate;

Disposing a beam splitter over a plurality of micro-LEDs, wherein the beam splitter comprises a plurality of stacked layers; and

A film comprising a plurality of quantum dots is disposed over the beam splitter.

13. the method of claim 12, wherein each of the plurality of micro-LEDs is configured to emit light only in the blue wavelength range.

14. The method of claim 12 or 13, wherein providing the beam splitter comprises providing a composite laminate structure comprising the plurality of layers.

15. The method of claim 12 or 13, wherein providing the beam splitter comprises providing a plurality of stacked film layers formed of extruded polymer.

16. The method of claim 12 or 13, wherein providing the beam splitter comprises depositing a layer of material using Chemical Vapor Deposition (CVD).

17. The method of claim 12 or 13, wherein providing the beam splitter comprises depositing a layer of material using Atomic Layer Deposition (ALD).

18. The method of claim 16 or 17, wherein the material comprises titanium dioxide, tantalum pentoxide, or silicon dioxide.

19. The method of any of claims 12-18, wherein disposing the membrane comprises: a first layer, a second layer, and a bonding material between the first layer and the second layer are provided, the bonding material comprising quantum dots.

20. The method of any of claims 12 to 19, wherein the plurality of layers are arranged such that the beam splitter transmits at least 90% of light having a wavelength between 400nm and 480nm and reflects at least 90% of light having a wavelength between 500nm and 800 nm.

21. The method of any of claims 12-20, wherein the forming comprises: the plurality of micro LEDs are formed in an array.

22. The method of any one of claims 12 to 21, wherein disposing the membrane comprises: a film is provided having quantum dots configured to emit light in a green wavelength range, and quantum dots configured to emit light in a red wavelength range.

Technical Field

The present application relates to display devices comprising high luminescence Quantum Dots (QDs) comprising a core/shell structure.

Background

Quantum dots can be used in display devices to produce vivid colors and have reduced cost due to the use of fewer electronic devices. Typically, all of the red, green, and blue light sources must be used to produce various colors on the screen, or a white light source is used with various color filtering methods to produce a color gamut. Both approaches require a large amount of electronics and become particularly expensive in larger displays.

Quantum Dots (QDs) have the unique ability to emit light at a single spectral peak with a narrow linewidth, thereby generating highly saturated colors. The emission wavelength can be tuned based on the size of the QDs. This ability to tune the emission wavelength enables display engineers to custom design spectra to maximize the efficiency and color performance of the display.

The size-dependent properties of QDs are used to produce QD films. The QD film may be used as a color down conversion layer in a display device. The use of a color down conversion layer in an emissive display may improve system efficiency by converting white or blue light to redder, greener, or both before the light passes through a color filter. This use of a color down conversion layer can reduce the loss of light energy due to filtering.

QDs can be used as a conversion material due to their broad absorption and narrow emission spectra. However, QDs emit light isotropically (i.e., in all directions), and thus much of the emitted light is not directed toward the front of the display device to be viewed. This limits the light output of the device and its overall efficiency.

disclosure of Invention

Therefore, there is a demand for improving the quality of the display device. Embodiments disclosed herein may be used to overcome the above-mentioned limitations of display devices, particularly limitations that may arise when quantum dots are used in display devices based on micro LED technology.

According to one embodiment, a lighting device includes a substrate having a plurality of micro LEDs, a beam splitter, and a film having a plurality of quantum dots. The beam splitter includes a plurality of layers and is disposed between the substrate and the film.

According to one embodiment, each of the plurality of micro-LEDs emits light only in the blue wavelength range.

According to one embodiment, the substrate is a flexible substrate.

according to one embodiment, the film includes a first layer, a second layer, and a bonding material disposed between the first layer and the second layer, the bonding material comprising quantum dots.

According to one embodiment, the plurality of layers are arranged such that the beam splitter transmits at least 90% of light having a wavelength between 400nm and 480nm and reflects at least 90% of light having a wavelength between 500nm and 800 nm.

According to one embodiment, the plurality of layers of the beam splitter comprise titanium dioxide, tantalum pentoxide, or silicon dioxide.

According to one embodiment, the thickness of the beam splitter is between 1 μm and 1 μm.

According to one embodiment, the substrate is a surface area of less than 750cm²A die of (a).

According to one embodiment, the plurality of quantum dots includes quantum dots that emit light in a green wavelength range and quantum dots that emit light in a red wavelength range.

According to one embodiment, the beam splitter comprises a composite laminate structure comprising a plurality of layers.

According to one embodiment, a method of manufacturing a lighting device comprises: forming a plurality of micro-LEDs on a substrate; and disposing a beam splitter over the plurality of micro LEDs. The beam splitter includes a plurality of stacked layers. The method further comprises the following steps: a film comprising a plurality of quantum dots is disposed over the beam splitter.

According to one embodiment, disposing the beam splitter includes depositing the layer of material using Chemical Vapor Deposition (CVD).

According to one embodiment, providing the beam splitter includes depositing the layer of material using Atomic Layer Deposition (ALD).

According to one embodiment, the material deposited by CVD or ALD comprises titanium dioxide, tantalum pentoxide or silicon dioxide.

According to one embodiment, the forming includes forming a plurality of micro-LEDs in an array.

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 present invention is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Other embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein.

Drawings

The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate embodiments of the present invention and, together with the description, further serve to explain the principles of the embodiments of the invention and to enable a person skilled in the pertinent art to make and use the embodiments.

fig. 1 illustrates an example lighting device using a Quantum Dot (QD) layer.

Fig. 2 illustrates an example illumination device using a QD layer and a beam splitter, according to one embodiment.

Fig. 3 illustrates another example illumination device using a QD layer and a beam splitter, according to an embodiment.

Figure 4 illustrates a layer structure of a beam splitter according to one embodiment.

Fig. 5 is a flow chart of manufacturing a lighting device according to one embodiment.

Fig. 6 illustrates an example structure of a QD according to an embodiment.

Fig. 7 illustrates an example QD film according to one embodiment.

The features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which like reference characters designate 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 or digits in the corresponding reference number. The drawings provided throughout this disclosure should not be construed as being drawn to scale unless otherwise indicated.

Detailed Description

Although specific configurations and arrangements may be discussed, it should be understood that this is done for illustrative purposes only. One skilled in the relevant art will recognize that other configurations and arrangements can be used without departing from the spirit and scope of the invention. It will be apparent to those skilled in the relevant art that the present invention may be used in a variety of other applications, in addition to those specifically mentioned herein.

It is noted that references in the specification to "one 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 are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is 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.

In this specification, all numbers expressing quantities of materials, ratios, physical properties of materials, and/or uses are to be understood as being modified by the word "about" unless otherwise expressly indicated.

As used herein, the term "about" means that a given amount of a value varies by ± 10% of the value, or optionally varies by ± 5% of the value, or varies by ± 1% of the value described in some embodiments. For example, "about 100 nm" encompasses a size range from 90nm to 110nm (inclusive).

As used herein, the term "nanostructure" refers to a structure having at least one region or characteristic dimension that is less than about 500nm in size. In some embodiments, the size of the nanostructures is less than about 200nm, less than about 100nm, less than about 50nm, less than about 20nm, or less than about 10 nm. Typically, the region or feature dimension will be along the smallest axis of the structure. Examples of such structures include nanowires, nanorods, nanotubes, branched nanostructures, nanotods, tripods, bipods, nanocrystals, nanodots, QDs, nanoparticles, and the like. The nanostructures can be, for example, substantially crystalline, substantially single crystalline, polycrystalline, amorphous, or a combination thereof. In some embodiments, each of the three dimensions of the nanostructure has a size of less than about 500nm, less than about 1200nm, less than about 100nm, less than about 50nm, less than about 20nm, or less than 10 nm.

As used herein, the term "QD" or "nanocrystal" refers to a nanostructure that is substantially single crystalline. Nanocrystals have at least one region or characteristic dimension that is less than about 500nm in size, and down to the order of less than about 1 nm. The terms "nanocrystal," "QD," "nanodot," and "dot" are readily understood by the ordinarily skilled artisan to refer to similar structures and are used interchangeably herein. The present invention also contemplates the use of polycrystalline or amorphous nanocrystals.

When used in reference to nanostructures, the term "heterostructure" refers to a nanostructure characterized by at least two different and/or distinguishable material types. Typically, one region of the nanostructure includes a first material type, and a second region of the nanostructure includes a second material type. In certain embodiments, the nanostructures comprise a core of a first material and at least one shell of a second (or third, etc.) material, wherein the different material types are radially distributed around, for example, the long axis of the nanowire, the long axis of the arms of the branched nanowire, or the center of the nanocrystal. The shell may, but need not, completely cover adjacent material to be considered a shell, or for nanostructures to be considered heterostructures; for example, a nanocrystal characterized by a core of one material covered by small islands of a second material is a heterostructure. In other embodiments, different material types are distributed at different locations within the nanostructure; for example along the major axis (long axis) of the nanowire, or along the long axis of the arm of the branch nanowire. Different regions within a heterostructure may comprise completely different materials, or different regions may comprise a base material (e.g., silicon) with different dopants or different concentrations of the same dopant.

As used herein, the term "diameter" of a nanostructure refers to the diameter of a cross-section perpendicular to a first axis of the nanostructure, where the first axis has the greatest difference in length relative to second and third axes (the second and third axes being the two axes with the closest length). The first axis is not necessarily the longest axis of the nanostructure; for example, for a disc-shaped nanostructure, the cross-section would be a substantially circular cross-section perpendicular to the short longitudinal axis of the disc. In the case where the cross-section is not circular, the diameter is the average of the major and minor axes of the cross-section. For elongated or high aspect ratio nanostructures, such as nanowires, the diameter is measured in a cross-section perpendicular to the longest axis of the nanowire. For spherical nanostructures, the diameter is measured from side to side through the center of the sphere.

The term "crystalline" or "substantially crystalline" when used with respect to nanostructures refers to the fact that the following nanostructures typically exhibit long-range order in one or more dimensions of the structure. Those skilled in the art will appreciate that the term "long-range order" will depend on the absolute size of the particular nanostructure, as the order of a single crystal cannot extend beyond the grain boundaries. In this case, "long-range order" would mean having substantial order in at least a majority of the dimensions of the nanostructure. In some cases, the nanostructures may carry an oxide or other coating, or may comprise a core and at least one shell. In this case, it is understood that the oxide, shell or shells, or other coating may, but need not, exhibit such ordering (e.g., it may be amorphous, polycrystalline, or otherwise). In this case, the phrases "crystalline," "substantially monocrystalline," or "monocrystalline" refer to the central core (excluding the coating or shell) of the nanostructure. The term "crystalline" or "substantially crystalline" as used herein is intended to also encompass structures comprising various defects, stacking faults, atomic substitutions, and the like, so long as the structure exhibits substantial long-range order (e.g., order over at least about 80% of the length of at least one axis of the nanostructure or core thereof). In addition, it will be understood that the interface between the core and the exterior of the nanostructure, or between the core and an adjacent shell, or between the shell and a second adjacent shell, may comprise amorphous regions, and may even be amorphous. As defined herein, this does not prevent the nanostructure from being crystalline or substantially crystalline.

The term "single crystal" when used with respect to a nanostructure means that the nanostructure is substantially crystalline and includes substantially single crystals. When used with respect to a nanostructure heterostructure comprising a core and one or more shells, "single crystal" means that the core is substantially crystalline and comprises a substantially single crystal.

As used herein, the term "ligand" refers to a molecule (whether weak or strong) that is capable of interacting with one or more faces of a nanostructure, for example, by covalent, ionic, van der waals forces, or other molecular interactions with the surface of the nanostructure.

As used herein, the term "quantum yield" (or QY) refers to the ratio of photons emitted to photons absorbed, for example, by a nanostructure or group of nanostructures. As is known in the art, quantum yield is typically determined by comparative methods using well-characterized standard samples with known quantum yield values.

As used herein, the term "dominant emission peak-to-peak wavelength" refers to the wavelength at which the emission spectrum exhibits the highest intensity.

Quantum dot lighting device

Fig. 1 shows an exemplary illumination device 100. The illumination apparatus 100 includes: a plurality of light sources 104 on the substrate 102; and a Quantum Dot (QD) film 106 disposed over light source 104. Details of QD film 106 and the QDs within QD film 106 are provided below, and these are not the focus of the embodiments described herein. Light source 104 may be a Light Emitting Diode (LED) that emits light at a lower wavelength (i.e., higher energy) than light emitted by quantum dots in QD film 106. For example, light source 104 may emit light in the blue wavelength range (i.e., one or more wavelengths between about 440nm and about 470 nm), while QDs within QD film 106 include: a first plurality of QDs that absorb blue light and emit light in the green wavelength range (i.e., one or more wavelengths between about 520nm and about 550 nm); and a second plurality of QDs that absorb blue light and emit light in the red wavelength range (i.e., one or more wavelengths between about 620nm and about 650 nm).

As a result of the light conversion performed by the QDs, emitted light 108 includes light in the blue wavelength range from light source 104 that is not absorbed by QD film 106, and light in the green and red wavelength ranges emitted from QDs within QD film 106. Thus, three primary colors are generated and can be filtered and combined downstream to produce any color. The filtering components are not shown for clarity and are not critical to the present embodiment.

The illumination configuration of fig. 1 suffers from light loss due to unwanted scattering and absorption. The isotropic emission of QDs within QD film 106 means that about half of the emitted light is directed back to substrate 102 where it is absorbed or scattered by substrate 102 and light source 104. As a result, the overall efficiency of the lighting device is reduced due to the loss of useful emitted light.

Fig. 2 shows a lighting device 200 according to an embodiment. Illumination device 200 includes beam splitting element 202 between QD film 106 and light source array 204. The light sources 204 may be designed such that they emit light only in the blue wavelength range. The beam splitting element 202 may be a dichroic beam splitter comprising a plurality of stacked material layers selected so as to allow certain wavelengths to pass while reflecting other wavelengths. In the illustrated embodiment, the beam splitting element 202 is a movable element, such as a composite laminate structure, that includes stacked layers of material. In another example, the beam splitting element 202 includes a plurality of stacked films formed from extruded polymer layers, such as acrylic polymers. The total thickness of the stacked films may be less than 100 μm, thereby allowing the beam splitting element 202 to be highly flexible.

The beam splitting element 202 may be designed such that light in the blue wavelength range is allowed to pass while light in the red and green wavelength ranges is reflected. For example, the transmission spectrum of the beam-splitting element 202 includes a transmission between 95% and 100% for wavelengths less than about 490nm, and a transmission between less than 3% for wavelengths greater than about 500 nm. For wavelengths greater than about 500nm, almost all of the light is reflected. In view of these optical properties, light in the blue wavelength range generated from the light source 204 will pass through the beam splitting element 202 with low loss, while light in the red and green wavelength ranges emitted from the QDs within the QD film 106 will be reflected back to the front end of the illumination device 200 (e.g., towards the user in the example where the illumination device 200 is a display). As a result, the emitted light 206 has a greater light output than the emitted light 108 from fig. 1. Due to the presence of the beam splitting element 202, the overall efficiency of the illumination device 200 may be increased by more than 80% compared to the illumination device 100.

Fig. 3 shows another lighting device 300 according to an embodiment. Illumination apparatus 300 includes QD film 106 and light source 204 with thin film beam splitter 302 deposited over substrate 102 and light source 204. Pellicle beam splitter 302 may represent a plurality of stacked pellicle films designed to allow certain wavelengths to pass while reflecting other wavelengths. Pellicle beam splitter 302 may include similar optical characteristics as beam splitting element 202. The total thickness of pellicle beam splitter 302 may be between about 1 μm and 50 μm. The result of using the thin film beam splitter 302 is that the emitted light 304 has a much greater light output than the emitted light 108 from FIG. 1.

The thin film beamsplitter 302 can be deposited over the substrate 102 and the light source 204 using a variety of methods. In one example, thin film beam splitter 302 is deposited using Atomic Layer Deposition (ALD). In another example, the thin film beamsplitter 302 is deposited using Chemical Vapor Deposition (CVD). The CVD process may be Plasma Enhanced (PECVD), or performed at a lower pressure than typical CVD processes (LPCVD). In yet another example, thin film beam splitter 302 is deposited using sputtering. Either example technique may be used to deposit each material layer in sequence to create the layer stack that makes up pellicle beam splitter 302.

Both pellicle beam splitter 302 and beam splitting element 202 may not be suitable for use in large display devices, such as large screen televisions and monitors. This is primarily due to the high cost of manufacturing such components and the limitation of depositing pellicle beamsplitter 302 over a large area. Thus, the lighting device 200 and the lighting device 300 may be used for smaller electronic screens, such as those found on watches, cell phones, PDAs, remote controls, portable gaming systems, and toys. In one embodiment, the surface area (i.e., die size) of the substrate 102 may be less than about 750cm²Less than about 500cm²Or less than about 100cm². In one embodiment, the substrate 102 is a flexible substrate made of a polymeric material such as, for example, Polyester (PET), Polyimide (PI), polyethylene naphthalate (PEN), or Polyetherimide (PEI).

The optical properties of the pellicle beam splitter 302 and the beam splitter element 202 may be highly temperature dependent. As such, heat generated from the light source 204 may adversely affect the ability of the pellicle beam splitter 302 and the beam splitting element 202 to perform as intended. Typical LEDs generate too much heat to be used as light sources 204. According to one embodiment, the light source 204 includes a plurality of micro LEDs. Micro LEDs are distinguished from typical LEDs or Organic Light Emitting Diodes (OLEDs). The micro-LEDs are fabricated in an array format, wherein each individual micro-LED has a maximum dimension in a range between about 1 μm and about 10 μm. Micro LEDs are also primarily made of gallium nitride (GaN) or indium gallium nitride (InGaN). Due to their small size and design, micro-LEDs dissipate much less heat and thus can be effectively used with pellicle beam splitter 302 or beam splitting element 202 without adversely affecting their optical performance. Example manufacturing details of micro LEDs may be found in U.S. patent No. 9,019,595, the disclosure of which is incorporated herein by reference.

One advantage of using pellicle beam splitter 302 is that its fabrication process may be integrated with the fabrication process of the micro LEDs. For example, similar tooling may be used to fabricate the micro-LEDs and thin film layers making up pellicle beam splitter 302, making the overall fabrication less expensive and complex.

FIG. 4 illustrates an exemplary beam splitter 400 according to one embodiment. The beam splitter 400 may represent the pellicle beam splitter 302 or the beam splitting element 202. Beam splitter 400 includes multiple layers, with the lowermost layer identified as layer 402-1 and the uppermost layer identified as layer 402-n. The thickness and refractive index of each of the layers 402-1 through 402-n are selected to provide the optical characteristics of the beam splitter 400. According to one embodiment, beam splitter 400 includes alternating layers of high and low refractive index material. According to one embodiment, beam splitter 302 includes between 50 and 500 layers, each layer having a thickness between about 50nm and about 100 nm. An example material for each layer 402-1 to 402-n includes titanium dioxide (TiO)₂) Tantalum pentoxide (Ta)₂O₅) And silicon dioxide (SiO)₂)。

According to one embodiment, the refractive index and thickness of each layer 402-1 to 402-n is selected such that beam splitter 400 transmits light having a wavelength less than about 490 (e.g., light in the blue wavelength range) while reflecting light having a wavelength greater than about 500nm (e.g., light in the red and green wavelength ranges).

Fig. 5 illustrates an example manufacturing method 500 for a lighting device. The method 500 may be performed as part of a large scale process for manufacturing an electronic device. Method 500 is not intended to be exhaustive and other steps may be performed without departing from the scope or spirit of the present invention. Additionally, the various steps of method 500 may be performed in a different order than that shown.

At step 502, micro LEDs are formed on a substrate. The substrate may be a semiconductor substrate. The substrate may be flexible. The micro LEDs may be formed as an array, with each micro LED pixel having a maximum dimension between about 1 μm and 10 μm.

At step 504, a beam splitter is positioned over the micro LEDs. The beam splitter may be a separate element, such as a laminated compound or extruded polymer material comprising multiple film layers, or the beam splitter may be a stack of layers deposited sequentially over the micro-LEDs. These layers may be deposited using a variety of techniques, such as ALD, CVD, and sputtering.

At step 506, a layer of quantum dots is disposed over the beam splitter. The quantum dot layer may be disposed in a Quantum Dot Enhanced Film (QDEF), as described in more detail below. The quantum dot layer may be provided as a separate element, or it may be a layer deposited over the beam splitter. For example, the QDs may be suspended in an amino silicone liquid and then spun or cast over the beam splitter. Other materials that may be used to suspend the QDs are discussed in detail below.

Exemplary embodiments of QD structures

Provided herein is a description of an example structure of a single QD. Such QDs may be used within QD film 106.

Fig. 6 shows a cross-sectional structure of a QD 600 coated with a barrier layer according to an embodiment. Barrier coated QD 600 includes QD601 and barrier 606. QD601 includes a core 602 and a shell 604. The core 602 includes a semiconductor material that emits light when absorbing higher energy. Examples of semiconductor materials for core 602 include indium phosphide (InP), cadmium selenide (CdSe), zinc sulfide (ZnS), lead sulfide (PbS), indium arsenide (InAs), indium gallium phosphide (InGaP), cadmium zinc selenide (CdZnSe), zinc selenide (ZnSe), and cadmium telluride (CdTe). Any other II-VI, III-V, ternary or quaternary semiconductor structure having a direct bandgap may also be used. In one embodiment, the core 602 may also include one or more dopants, such as metals, alloys, to provide some examples. Examples of the metal dopant may include, but are not limited to, zinc (Zn), copper (Cu), aluminum (Al), platinum (Pt), chromium (Cr), tungsten (W), palladium (Pd), or a combination thereof. The presence of one or more dopants in the re-core 602 may improve the structural and optical stability and Quantum Yield (QY) of the QDs 601 compared to undoped QDs.

According to one embodiment, the diameter of the core 602 may be less than 20 nm. In another embodiment, the diameter of the core 602 may be sized between about 1nm to about 5 nm. The ability to tailor the size of the core 602, and thus the size of the QDs 601 in the nanometer range, enables light emission coverage throughout the spectrum. Generally, larger QDs emit light towards the red end of the spectrum, while smaller QDs emit light towards the blue end of the spectrum. This effect is due to the fact that larger QDs have energy levels that are closer together than smaller QDs. This allows the QDs to absorb photons containing less energy, i.e., photons near the red end of the spectrum.

A shell 604 surrounds the core 602 and is disposed on an outer surface of the core 602. The shell 604 may include cadmium sulfide (CdS), cadmium zinc sulfide (ZnCdS), zinc selenide sulfide (ZnSeS), zinc selenide (ZnSe), and zinc sulfide (ZnS). In one embodiment, the shell 604 may have a thickness of, for example, one or more monolayers. In other embodiments, the shell 604 may have a thickness between about 1nm to about 5 nm. The shell 604 may be used to help reduce lattice mismatch with the core 602 and improve the QY of the QD 601. The shell 604 may also help passivate and remove surface trap states, such as dangling bonds, on the core 602 to increase the QY of the QD 601. The presence of surface trap states may provide non-radiative recombination centers and help to reduce the emission efficiency of the QDs 601.

In alternative embodiments, QD601 may include a second shell disposed on shell 604, or more than two shells surrounding core 602, without departing from the spirit and scope of the present invention. In one embodiment, the thickness of the second shell may be of the order of two monolayers, and although not required, the second shell is also typically a semiconductor material. The second shell may provide protection for the core 602. The second shell material may be zinc sulfide (ZnS) or zinc selenide (ZnSe), although other materials may be used without departing from the scope or spirit of the invention.

The barrier layer 606 is configured to form a coating on the QDs 601. In one embodiment, the barrier layer 606 is disposed on and substantially in contact with the outer surface of the shell 604. In embodiments of QDs 601 having one or more shells, barrier layer 606 may be disposed on the outermost shell of QDs 601. In an example embodiment, the barrier layer 606 is configured to act as a spacer between the QDs 601 and one or more quantum dots, e.g., in a solution, composition, and/or film having a plurality of quantum dots, which may be similar to the QDs 601 and/or the QD 600 coated with the barrier layer. In such QD solutions, compositions of QDs, and/or QD films, barrier layer 606 may help prevent aggregation of QDs 601 with neighboring QDs. Aggregation of QD601 with neighboring QDs may result in an increase in the size of QD601 and, in turn, a decrease or quenching in the optical emission characteristics of aggregated QDs (not shown) including QD 601. As discussed above, the optical characteristics of QDs are size dependent, and therefore the increase in size of QDs due to aggregation leads to quenching phenomena. The barrier layer 606 may also prevent reabsorption of optical emissions from the QD solution, QD composition, and/or other QDs in the QD film by the QDs 601 and thus increase the QY of these QD solutions, QD compositions, and/or QD films. In further embodiments, barrier layer 606 provides protection for QDs 601 from, for example, moisture, air, and/or harsh environments (e.g., high temperatures and chemicals used during photolithographic processing of the QDs and/or during the fabrication process of QD-based devices) that may adversely affect the structural and optical properties of QDs 601.

The barrier layer 606 includes one or more materials that are amorphous, optically transparent, and/or electrically inert. Suitable barrier layers include inorganic materials such as, but not limited to, inorganic oxides and/or nitrides. According to various embodiments, examples of materials for barrier layer 606 include oxides and/or nitrides of Al, Ba, Ca, Mg, Ni, Si, Ti, or Zr. In various embodiments, the thickness of the barrier layer 606 may be in the range of about 8nm to about 15 nm. In some embodiments, the thickness of the barrier layer 606 may have a minimum value such that, for example, the center-to-center distance between two adjacent QDs 600 in a solution, composition, and/or film is equal to or greater than the foster radius (also known in the art as the foster distance) to reduce or substantially eliminate resonance energy transfer and/or reabsorption of optical emission between adjacent QDs 600 and thus increase the QY of adjacent QDs 600. In some embodiments, the thickness of the barrier layer 606 may have a minimum value between about 8nm and about 15 nm.

The forster radius may refer to the center-to-center distance between two adjacent QDs, such as QD 600, at which the resonance energy transfer efficiency between the two adjacent QDs is about 50%. A center-to-center distance between two neighboring QDs greater than the foster radius may reduce resonance energy transfer efficiency and improve the optical emission characteristics and QY of the neighboring QDs. The process of resonance energy transfer may occur when one QD in an electronically excited state transfers its excitation energy to a nearby or neighboring QD. The resonant energy transfer process is a non-radiative quantum mechanical process. Therefore, when resonance energy transfer occurs from one QD, the optical emission characteristics of one QD may be quenched, and the QY of one QD may be adversely affected.

According to one embodiment, as shown in fig. 6, the QD 600 coated with a barrier layer may additionally or optionally include a plurality of ligands or surfactants 608. According to one embodiment, ligands or surfactants 608 may be adsorbed or bound to the outer surface of the QD 600 coated with a barrier layer, for example on the outer surface of the barrier layer 606. The plurality of ligands or surfactants 608 can include a hydrophilic or polar head 608a and a hydrophobic or non-polar tail 608 b. A hydrophilic or polar head 608a may be bonded to the barrier layer 606. The presence of ligands or surfactants 608 may help to separate QD 600 and/or QD601 from other QDs during their formation, e.g., in solutions, compositions, and/or films. The quantum efficiency of QDs (e.g., QD 600 and/or QD 601) may degrade and quench the optical emission characteristics of these QDs if allowed to aggregate during their formation. Ligands or surfactants 608 may also be used to impart certain properties to the barrier coated QD 600, such as hydrophobicity, to provide miscibility in non-polar solvents, or to provide reaction sites (e.g., reverse micellar systems) for other compounds to bind.

There is a wide variety of ligands that can be used as ligand 608. In some embodiments, the ligand is a fatty acid selected from lauric acid, caproic acid, myristic acid, palmitic acid, stearic acid, and oleic acid. In some embodiments, the ligand is an organic phosphine or organic phosphine oxide selected from trioctylphosphine oxide (TOPO), Trioctylphosphine (TOP), Diphenylphosphine (DPP), triphenylphosphine oxide, and tributylphosphine oxide. In some embodiments, the ligand is an amine selected from the group consisting of dodecylamine, oleylamine, hexadecylamine, and octadecylamine. In some embodiments, the ligand is Trioctylphosphine (TOP). In some embodiments, the ligand is oleylamine. In some embodiments, the ligand is diphenylphosphine.

There is a wide variety of surfactants that can be used as the surfactant 608. A nonionic surfactant can be used as the surfactant 608. Some examples of nonionic surfactants include polyoxyethylene nonylphenyl ether (trade name IGEPAL CO-520), IGEPAL CO-630, IGEPAL CA-630, and Arkopal N100.

In some embodiments, QDs 601 and/or 600 may be synthesized to emit light in the red, orange, and/or yellow range. In some embodiments, QDs 601 and/or 600 may be synthesized to emit light in the green and/or yellow range. In some embodiments, QDs 601 and/or 600 may be synthesized to emit light in the blue, indigo, violet, and/or ultraviolet range. In some embodiments, QDs 601 and/or 600 may be synthesized to have a dominant emission peak wavelength between about 605nm and about 650nm, between about 510nm and about 550nm, or between about 300nm and about 480 nm.

QDs 601 and/or 600 may be synthesized to exhibit high QY. In some embodiments, QDs 601 and/or 600 may be synthesized to exhibit between 80% and 95%, or between 85% and 90% QY.

Thus, according to various embodiments, QDs 600 may be synthesized such that the presence of blocking layer 606 over QDs 601 does not substantially alter or quench the optical emission characteristics of QDs 601.

QY of QDs can be calculated using an organic dye as a reference (e.g., rhodamine 640 as a reference for red emitting QDs 601 and/or 600 at 540nm excitation wavelength, a fluorescein dye as a reference for green emitting QDs 601 and/or 600 at 440nm excitation wavelength, diphenylanthracene as a reference for blue emitting QDs 601 and/or 600 at 355nm excitation wavelength) based on the following formula:

Subscripts ST and X denote the standard (reference dye) and core/shell QD solution (test sample), respectively. Phi_XIs the quantum yield of core/shell QDs, and phi_STIs the quantum yield of the reference dye. (I/a), wherein I is the area under the emission peak (wavelength scale); a is the absorbance at the excitation wavelength and η is the refractive index of the reference dye or core/shell QD in the solvent. See, e.g., WillIAms et al (1983) "Relative fluorescence yield values used a computerised luminescence spectrometer" analysis 108: 1067. The references listed in Williams et al are for QDs with green and red emission.

Exemplary Quantum dot enhancement films

Fig. 7 shows an example of a Quantum Dot Enhanced Film (QDEF) 700. QDEF 700 is one example of QD film 106. The quantum dot enhancement film 700 includes a bottom layer 704, a top layer 706, and a quantum dot layer 702 sandwiched therebetween.

The bottom layer 704 and the top layer 706 can be various materials that are substantially transparent to visible wavelengths (e.g., 400-700 nm). For example, the bottom layer 704 and the top layer 706 can be glass or polyethylene terephthalate (PET). The bottom layer 704 and the top layer 706 may also be made of alumina coated polyester. Other polymers may also be used that exhibit low oxygen permeability and low absorbance for wavelengths emitted by the quantum dots and trapped within quantum dot layer 702. The bottom layer 704 and the top layer 706 need not comprise the same material.

Quantum dot layer 702 includes a plurality of quantum dots within an adhesive material. According to one embodiment, quantum dot layer 702 has a thickness between about 50 and 150 micrometers (μm) and is used as an optical down conversion layer. The quantum dot layer 702 may have a thickness of about 100 μm. The adhesive material bonds to both the bottom layer 704 and the top layer 706, thereby holding the sandwich-like structure together.

In one embodiment, the plurality of quantum dots comprise a size that emits in at least one of the green and red visible wavelength spectra. The quantum dots in quantum dot layer 702 are protected from the environment and remain separated from each other to avoid quenching. The quantum dots can be spaced apart a sufficient distance such that quenching processes such as excited state reactions, energy transfer, complex formation, and collision quenching do not occur.

In one example, quantum dots are mixed in an amino silicone fluid and emulsified in an epoxy resin that is applied to form quantum dot layer 702. Other example materials for quantum dot layer 702 include acrylates, epoxies, acrylated epoxies, ethylene vinyl acetate, thiol-enes, polyurethanes, polyethers, polyols, and polyesters. Further details regarding the fabrication and operation of quantum dot enhanced films can be found in U.S. patent No. 9,199,842, the disclosure of which is incorporated herein by reference.

It should be understood that the detailed description section, and not the summary and abstract sections, is intended to be used to interpret the claims. The summary section and abstract section may set forth one or more, but not all exemplary embodiments of the invention as contemplated by the inventors, and are therefore not intended to limit the invention and the appended claims in any way.

The invention has been described above with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. Boundaries of these functional components have been arbitrarily defined herein for convenience of description. Alternate boundaries may be defined so long as the specified functions and relationships thereof are appropriately performed.

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.

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.