阅读说明：本技术 用于滤色器应用的量子点构造 (Quantum dot construction for color filter applications ) 是由 奈杰尔·L·皮克特 詹姆斯·哈里斯 玛格丽特·海因斯 约瑟夫·泰勒 于 2018-07-05 设计创作，主要内容包括：有机加帽量子点通过以下方式制备：用6?巯基己醇(MCH)和2?[2?(2?甲氧基乙氧基)?乙氧基]?乙酸(MEEAA)的组合将多种构造的QD的表面官能化。这样的MCH/MEEAA加帽的QD表现出改善的与在制造发光装置如液晶显示器的含QD膜中使用的溶剂的相容性。(The organic capped quantum dots are prepared by the following method: the surface of the variously structured QDs was functionalized with a combination of 6-Mercaptohexanol (MCH) and 2- [2- (2-methoxyethoxy) -ethoxy ] -acetic acid (MEEAA). Such MCH/MEEAA capped QDs exhibit improved compatibility with solvents used in the manufacture of QD-containing films for light emitting devices such as liquid crystal displays.)

1. A quantum dot, comprising:

a kernel;

a layer substantially surrounding the inner core; and

6-Mercaptohexanol (MCH) and 2- [2- (2-methoxyethoxy) -ethoxy ] -acetic acid (MEEAA) capping ligand.

2. The quantum dot of claim 1, wherein the layer consists essentially of a direct bandgap semiconductor that absorbs light at a wavelength between about 430nm to about 470 nm.

3. The quantum dot of claim 1 or claim 2, wherein the core comprises indium and phosphorus.

4. The quantum dot of any one of claims 1 to 3, wherein the inner core comprises an alloyed or doped derivative of InP.

5. The quantum dot of claim 4, wherein the core comprises InPZnS.

6. The quantum dot of claim 4, wherein the core comprises InPZnSeS.

7. The quantum dot of any one of claims 1 to 6, wherein the layer comprises a metal chalcogenide.

8. The quantum dot of claim 7, wherein the metal chalcogenide is any one of ZnS, ZnSe, ZnSeS and ZnO.

9. The quantum dot of any one of claims 1 to 8, wherein the layer substantially surrounding the core comprises three or more monolayers less than or equal to fifteen.

10. A composition comprising a plurality of quantum dots according to any one of claims 1 to 8 dispersed in Propylene Glycol Monoethyl Ether Acetate (PGMEA).

11. A quantum dot, comprising:

an inner core comprising indium and having a first bandgap;

a first layer substantially surrounding the core and comprising a first metal chalcogenide having a second band gap larger than the first band gap; and

a second layer on the first layer, the second layer including a second metal chalcogenide having a third band gap larger than the second band gap,

wherein the first layer comprises more than three and less than or equal to fifteen monolayers of the first metal chalcogenide.

12. The quantum dot of claim 11, wherein the quantum dot has an in-rod dot type configuration.

13. The quantum dot of claim 12, wherein the inner core is longitudinally displaced from a center of the rod.

14. The quantum dot of any one of claims 11 to 13, wherein the core further comprises phosphorus.

15. The quantum dot of any one of claims 11 to 14, wherein the inner core comprises an alloyed or doped derivative of InP.

16. The quantum dot of claim 15, wherein the core comprises InPZnS.

17. The quantum dot of claim 15, wherein the core comprises InPZnSeS.

18. The quantum dot of any one of claims 11 to 17, wherein at least one of the first and second metal chalcogenides is any one of ZnS, ZnSe, ZnSeS s and ZnO.

19. A quantum dot-quantum well semiconductor nanoparticle, the quantum dot-quantum well semiconductor nanoparticle comprising:

a core comprising a first metal chalcogenide having a first band gap;

a first layer substantially surrounding the core and comprising indium and having a second bandgap smaller than the first bandgap;

a second layer substantially surrounding the first layer and comprising a second metal chalcogenide and having a third band gap substantially equal to the first band gap;

a third layer substantially surrounding the second layer and comprising a third metal chalcogenide having a third band gap larger than the first band gap and the second band gap,

wherein the second layer comprises more than three and less than or equal to fifteen monolayers of the first metal chalcogenide.

20. The quantum dot-quantum well semiconductor nanoparticle of claim 19, wherein the first metal chalcogenide and the second metal chalcogenide are different metal chalcogenides.

21. The quantum dot-quantum well semiconductor nanoparticle of claim 19 or claim 20, wherein the first metal chalcogenide and the third metal chalcogenide are the same metal chalcogenide.

22. A Liquid Crystal Display (LCD), comprising:

a light source in the blue portion of the visible spectrum;

a color filter array in optical communication with the blue light source and containing a plurality of quantum dots according to any one of claims 1 to 9.

23. A Liquid Crystal Display (LCD), comprising:

a light source in the blue portion of the visible spectrum;

a color filter array in optical communication with the blue light source and containing a plurality of quantum dots according to any one of claims 11 to 18.

24. A Liquid Crystal Display (LCD), comprising:

a light source in the blue portion of the visible spectrum;

a color filter array in optical communication with the blue light source and containing a plurality of quantum dot-quantum well semiconductor nanoparticles according to any one of claims 19 to 21.

1. The field of the invention.

The present invention generally relates to electronic displays. More particularly, the present invention relates to the use of semiconductor nanoparticles ("quantum dots") in luminescent color filters for Liquid Crystal Displays (LCDs).

2.Including a description of the related art in light of the information disclosed in 37 CFR 1.97 and 1.98.

In order for a display technology to display a range of colors, it is necessary to be able to switch the output of multiple pixels or sub-pixels of different colors so that the resulting combination of color outputs adds up to the perception of a composite color by a viewer. For example, a magenta color may be generated by two adjacent pixels displaying blue and red colors, and the hue may be changed by adjusting the relative intensities of the blue and red light components.

The method of adjusting or switching the pixel intensity varies from display technology to display technology, as does the method of producing red, green, and blue primary color sub-pixels. In the case of Liquid Crystal Displays (LCDs) or white-oled (woled) -like displays, the displays employ a white backlight that is filtered by red, green, and blue color filters to produce a primary light output.

One area of increasing interest is the use of Quantum Dots (QDs) in emissive color filters for LCDs. To better understand this concern, a brief discussion of how an LCD works is needed. The way in which LCDs can switch or adjust light intensity relies on the use of a complex stack of optical films using liquid crystal cells (liquid crystal cells) between crossed polarizers. The backlight unit produces unpolarized white light that enters the liquid crystal cell through a linear polarizer. When a voltage is applied to the liquid crystal cell, this results in a change in crystal alignment and a rotation of the linearly polarized white light, which then passes through the color filter, and the transmitted light (which now has the appropriate polarization) exits the display via a second linear polarizer arranged orthogonal to the first polarizer. When no voltage is applied, the liquid crystals are not aligned in such a way that the incident polarized light is rotated. After transmission through the color filter, the transmitted light still has the initial polarization and is therefore blocked from exiting the system by the second linear polarizer.

The operation of an LCD critically depends on controlling the polarization of the light, and therefore scattering within the system should be minimized, as any scattering may result in depolarization of the light, resulting in reduced contrast. An example of this is when the pixel is off, the liquid crystal does not rotate the light, so it should not be able to leave the system because it is rejected by the second polarizer. However, if there is some scattering and depolarization of the light, a portion of the depolarized light may have a polarization suitable for exit, and thus cause pixel filtered-through and lost contrast.

As briefly mentioned above, LCDs employ a white backlight that is filtered through red, green and blue color filters to produce RGB pixel primary color light outputs. However, this method of generating the RGB primaries is not the most efficient approach, because in each case a large amount of light is filtered out. For example, to form the primary color red, the green and blue portions of the backlight must be filtered, for green, the red and blue portions filtered, and so on.

The color performance of a display is typically discussed in terms of gamut size relative to the standard. In particular, the amount of overlap of the respective criteria is usually the most relevant information.

The width of the transmission window is important because it determines how much unwanted light can leak and directly affect the saturation of the RGB primaries of the display device and the resulting color performance. To reduce the amount of leakage, manufacturers increase the optical density of the color filter so that it is less transmissive, which results in improved color at the expense of overall light transmission and display brightness.

Brief description of several figures

Fig. 1A and 1B show UV/visible absorption and emission spectra of CFQD quantum dots that emit green light (fig. 1A) and red light (fig. 1B).

Fig. 2A is a graphical representation of EQE versus% blue LED absorbance for CFQD quantum dots emitting green light.

Fig. 2B is a graphical representation of the peak emission wavelength of a CFQD quantum dot emitting green light versus the% blue LED absorbance.

Fig. 2C is a graphical representation of FWHM versus% blue LED absorbance for CFQD quantum dots emitting green light.

Fig. 2D is a graphical representation of absorbance versus concentration at 450nm for green emitting CFQD quantum dots in a film.

FIG. 3 is a schematic cross-sectional view of a prior art dot-in-rod-type (dot-in-rod-type) configuration.

Fig. 4 is a schematic of three different nanoparticle configurations and their corresponding energy level arrangements.

Fig. 5 is a schematic diagram of a related art Liquid Crystal Display (LCD) having a QD-containing backlight unit.

Fig. 6 is a schematic diagram of a Liquid Crystal Display (LCD) with QDs directly in the color filter.

Detailed Description

Background

The following description of the embodiments is merely exemplary in nature and is in no way intended to limit the subject matter of the disclosure, its application, or uses.

As used throughout, ranges are used as a shorthand notation for describing each and every value that is within the range. Any value within a range can be selected as the terminus of the range. Unless otherwise indicated, all percentages and amounts expressed herein and elsewhere in the specification are to be understood as being percentages by weight.

For the purposes of this specification and the appended claims, all numbers expressing quantities, percentages or proportions, and other numerical values used in the specification and claims, are to be understood as being modified in all instances by the term "about", unless otherwise indicated. The use of the term "about" applies to all numerical values, whether or not explicitly indicated. The term generally refers to a range of numbers that one of ordinary skill in the art would consider reasonably deviated from the recited values (i.e., having equivalent functionality or results). For example, this term can be construed to include deviations of ± 10%, alternatively ± 5%, alternatively ± 1%, alternatively ± 0.5%, and alternatively ± 0.1% of a given value, provided that such deviations do not alter the ultimate function or result of that value. Accordingly, unless indicated to the contrary, the numerical parameters set forth in this specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention.

It is noted that, as used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless expressly and unequivocally limited to one referent. As used herein, the term "include" and grammatical variations thereof are intended to be non-limiting such that recitation of items in a list is not to the exclusion of other like items that may be substituted or added to the listed items. For example, as used in this specification and the appended claims, the terms "comprising" (and forms, derivatives, or variants thereof, such as "comprising" and "comprises"), "including" (and forms, derivatives, or variants thereof, such as "including" and "includes") and "having" (and forms, derivatives, or variants thereof, such as "having" and "has") are inclusive (i.e., open-ended) and do not exclude additional elements or steps. Thus, these terms are intended to encompass not only the recited element or elements or step or steps, but also other elements or steps not explicitly recited. Furthermore, as used herein, the terms "a" or "an" when used in conjunction with an element can mean "one," but can also conform to the meaning of "more than one," at least one, "and" one or more than one. Thus, an element preceded by "a" or "an" does not exclude the presence of other identical elements, without further constraints.

QDs as luminescent color filters for converting blue backlights

Research aimed at using QDs as luminescent filters to convert blue backlights has been conducted in the past. One of the disadvantages of this embodiment is that for it to work well, 100% of the incident blue light must be absorbed and converted to provide the desired saturated color with an acceptable level of efficiency. At less than 100% absorbance, any unabsorbed blue light will be transmitted and degrade the color purity of the green or red pixels and adversely affect color performance.

Quantum dot materials [ nanotechnology Ltd., 46Grafion Street, Manchester M139 NT U.K.]With a strong overlap between exciton absorption and emission. As used herein, "CFQD quantum dots" means quantum dots of various diameters having an inner core comprising indium and phosphorus. In some cases, the CFQD quantum dot may also include one or more shells that at least partially cover the core. In some cases, at least one of the one or more housings comprises zinc. In some cases, at least one of the one or more shells comprises zinc, and any of sulfur, selenium, and oxygen. In some cases, at least one of the one or more shells comprises zinc, and one or more of sulfur, selenium, and oxygen. In some cases, CFQD quantum dots are broad wavelength absorbers and emitters of light with wavelengths in the visible spectrum of the red region. In some cases, CFQD quantum dots are broad wavelength absorbers and emitters of light with wavelengths in the visible spectrum of the green region. In some cases, CFQD quantum dots are broad wavelength absorbers and emitters of light with wavelengths in the yellow region of the visible spectrum. In some cases, the CFQD quantum dots are broad wavelength absorbers and wavesEmitters of light in the visible spectrum long in the orange region. In some cases, CFQD quantum dots are broad wavelength absorbers and emitters of light with wavelengths in the visible spectrum in the blue region.

Fig. 1A and 1B show absorption and emission spectra of green-emitting and red-emitting CFQD quantum dots, respectively. Accordingly, emission from CFQD quantum dots has a reasonable chance of being reabsorbed by another dot near the emitting dot or in the escape path of the luminescence. The significance of this is that the re-absorption effect becomes greater as the loading is increased to absorb all the blue light for color conversion.

The result of reabsorption is a reduction in conversion efficiency or External Quantum Efficiency (EQE), thereby reducing the full width at half maximum (FWHM) and red-shifting the emission. The FWHM narrowing and Photoluminescence (PL) red-shift are due to more light being reabsorbed on the short wavelength side of the emission peak. Fig. 2A-2D show how the EQE, peak wavelength, and FWHM vary with the% blue LED absorbance of green-emitting CFQD quantum dots (note: similar effects are observed for red CFQD quantum dots). In this case, the dots used have the following dilute solution optical specifications: PL-526.5 nm; FWHM 44 nm; PLQY ═ 79%; and the film thickness was 300 μm. The data show that from 40% absorbance to 80% EQE is small, after which it decreases as the absorbance increases. As the absorbance increases, the peak wavelength shows a more or less linear red shift, while as the absorbance increases, the FWHM initially decreases and then remains the same.

Therefore, there is a need for QD architectures with improved absorption at 450nm relative to exciton absorption.

Core/shell type QD with thick shells, quantum dot-quantum well, and rod-in-dot type QD architectures are known in the art. However, no specific compositions are described that facilitate their use as color changing media for color filter applications.

Core/shell type QDs with shells having a thickness of > 10 monolayers, so-called "giant" QDs, have been investigated because thick shells have been found to help make the optical properties of the QDs insensitive to environmental influences. For Cd-type QDs, in particular CdSe/CdS, thick shells have been studied, but there is no relevant report for Cd-free systems.

InP/ZnSe/ZnS QDs have been reported in the prior art. However, a ZnSe shell thickness of-1 monolayer would not be sufficient to significantly improve the absorption properties of QDs in the 450nm region.

Quantum dot-quantum well (QD-QW) configurations are known in the art, however, to the best of the applicant's knowledge, the combination of a QD-QW structure and a thick second shell has not been previously described.

The point-in-rod configuration (fig. 3) can minimize self-absorption. However, such nanoparticle constructions in the art include an anisotropic inner core. To the best of the applicant's knowledge, the use of an alloyed core in such a construction is not disclosed in the art.

Improved absorption and robustness at 430-470nm

The durability of core/shell QDs depends largely on the quality and thickness of the shell layer. The outer shell layer functions to electrically and physically isolate the core from the external environment. A thick energy and crystallographically compatible shell, which may be the first component of the quantum dot to be damaged upon exposure to harsh environments such as incompatible solvents, high heat, high light, high oxygen, or high humidity environments, can accomplish this and, if thick enough, can protect the inner core from ligand effects.

As discussed above, CFQD quantum dots have a strong overlap between the first exciton absorption and emission that can lead to side effects on conversion efficiency and wavelength shift when these dots are present in the very high concentrations required for this application. If the absorbance of the material in the range of 430 to 470nm, in some cases in the range of 440 to 460nm, and in some cases at about 450nm can be significantly increased relative to the first exciton absorption, this can achieve less reabsorption in the desired high-absorption color filter system. One way to achieve this is to grow a thick outer layer on quantum dots consisting of a direct bandgap semiconductor that absorbs at about 450 nm. Photons absorbed in this layer may generate excitons that may fall into the core quantum well where they may recombine and emit light. To achieve such a configuration, the outer layer material needs to have the appropriate bandgap energy, conduction and valence band offsets relative to the core, and have a compatible lattice constant to grow epitaxially on the core without creating excessive strain, as lattice strain may ultimately lead to a reduction in photoluminescence quantum yield (PLQY) and stability of these dots.

In some embodiments, the core of the quantum dot comprises indium and phosphorus. For example, suitable materials include, but are not limited to, InP and its alloyed or doped derivatives. In some cases, alloyed quantum dot cores comprising different amounts of In, P, Zn, and S may be used In accordance with aspects of the present disclosure. In other cases, alloyed quantum dot cores comprising different amounts of In, P, Zn, and Se may be used In accordance with aspects of the present disclosure. In other cases, alloyed quantum dot cores containing different amounts of In, P, Zn, S, and Se may be used In accordance with aspects of the present disclosure. In some cases, the alloyed quantum dot cores may contain different amounts of one or more of Ga and Al In addition to or instead of In.

In some cases, the alloyed quantum dot core may be doped with up to 5 atomic% of one dopant or a combination of dopants. In some cases, group I elements such as Li, Na, and K may be used as dopants. In some cases, group II elements such as Mg, Ca, and Sr may be used as dopants. In some cases, group III elements such as B, Al or Ga may be used. In some cases, transition metals may be used as dopants.

In some cases, QDs used in accordance with various aspects of the present disclosure may contain a core material comprising:

IIA-VIB (2-16) material consisting of a first element from group 2 of the periodic Table of the elements and a second element from group 16 of the periodic Table of the elements, and further including ternary and quaternary materials and dopant materials. Nanoparticle materials include, but are not limited to: MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe, BaS, BaSe, BaTe;

IIB-VIB (12-16) materials consisting of a first element from group 12 of the periodic Table of the elements and a second element from group 16 of the periodic Table of the elements, and also ternary and quaternary materials and doping materials. Nanoparticle materials include, but are not limited to: ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe;

II-V materials, which consist of a first element from group 12 of the periodic Table of the elements and a second element from group 15 of the periodic Table of the elements, and also ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: zn₃P₂、Zn₃As₂、Cd₃P₂、Cd₃As₂、Cd₃N2、Zn₃N₂；

III-V materials consisting of a first element from group 13 of the periodic table and a second element from group 15 of the periodic table, and further including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: BP, AlP, AlAs, AlSb; GaN, GaP, GaAs, GaSb; InN, InP, InAs, InSb, AlN, BN;

III-IV materials consisting of a first element from group 13 of the periodic table and a second element from group 16 of the periodic table, and also ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: b is₄C、Al₄C₃、Ga₄C；

III-VI materials consisting of a first element from group 13 of the periodic Table of the elements and a second element from group 16 of the periodic Table of the elements, and also including ternary and quaternary materials. Nanoparticle materials include, but are not limited to: al (Al)₂S₃、Al₂Se₃、Al₂Te₃、Ga₂S₃、Ga₂Se₃、In₂S₃、In₂Se₃、Ga₂Te₃、In₂Te₃、InTe；

IV-VI materials consisting of a first element from group 14 of the periodic Table of the elements and a second element from group 16 of the periodic Table of the elements, and further including ternary and quaternary materials toAnd a doping material. Nanoparticle materials include, but are not limited to: GeTe, PbS, PbSe, PbTe, Sb₂Te₃SnS, SnSe and SnTe; and

nanoparticle materials composed of a first element from any group of the transition metals of the periodic table and a second element from any group 16 of the periodic table, and also including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: NiS, CrS, CuInS₂、AgInS₂。

For the purposes of the specification and claims, the term doped nanoparticle refers to nanoparticles of the above materials and dopants consisting of one or more main group or rare earth elements, most commonly transition metals or rare earth elements, such as but not limited to zinc sulfide with manganese, such as with Mn²⁺Doped ZnS nanoparticles.

For the purposes of the specification and claims, the term "ternary material" refers to QDs that are the above and three component materials. The three components are generally a combination of elements from the mentioned groups, an example being (Zn)_xCd_x-1S)_mL_nNanocrystals (where L is a capping reagent).

For the purposes of the specification and claims, the term "quaternary material" refers to nanoparticles that are described above and are four-component materials. The four components are generally a combination of elements from the mentioned groups, an example being (Zn)_xCd_x-1S_ySe_y-1)_mL_nNanocrystals (where L is a capping reagent).

In most cases, the material used on any shell or subsequent number of shells grown on the core particles will be a material of similar lattice type to the core material, i.e. a material having a close lattice match to the core material so that it can be grown epitaxially on the core, but need not be limited to this compatibility. In most cases, the material used on any shell or subsequent number of shells grown on the core present will have a wider band gap than the core material, but need not be limited to this compatible material. In some cases, the material of any shell or subsequent number of shells grown on the core may include materials including:

IIA-VIB (2-16) material consisting of a first element from group 2 of the periodic Table of the elements and a second element from group 16 of the periodic Table of the elements, and further including ternary and quaternary materials and dopant materials. Nanoparticle materials include, but are not limited to: MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe, BaS, BaSe, BaTe;

IIB-VIB (12-16) materials consisting of a first element from group 12 of the periodic Table of the elements and a second element from group 16 of the periodic Table of the elements, and also ternary and quaternary materials and doping materials. Nanoparticle materials include, but are not limited to: ZnS, ZnSe, ZnSeS, ZnTe, ZnO, CdS, CdSe, CdTe, CdO, HgS, HgSe, HgTe, HgO;

II-V materials, which consist of a first element from group 12 of the periodic Table of the elements and a second element from group 15 of the periodic Table of the elements, and also ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: zn₃P₂、Zn₃As₂、Cd₃P₂、Cd₃As₂、Cd₃N₂、Zn₃N₂；

III-V materials consisting of a first element from group 13 of the periodic table and a second element from group 15 of the periodic table, and further including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: BP, AlP, AlAs, AlSb; GaN, GaP, GaAs, GaSb; InN, InP, InAs, InSb, A1N and BN;

III-IV materials consisting of a first element from group 13 of the periodic table and a second element from group 16 of the periodic table, and also ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: b is₄C、Al₄C₃、Ga₄C；

III-VI materials of the first element from group 13 of the periodic Table and of the second element from group 16 of the periodic TableBinary, and also ternary and quaternary materials. Nanoparticle materials include, but are not limited to: al (Al)₂S₃、Al₂Se₃、Al₂Te₃、Ga₂S₃、Ga₂Se₃、In₂S₃、In₂Se₃、Ga₂Te₃、In₂Te₃、InTe；

IV-VI materials consisting of a first element from group 14 of the periodic Table of the elements and a second element from group 16 of the periodic Table of the elements, and further including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: GeTe, PbS, PbSe, PbTe, Sb₂Te₃SnS, SnSe and SnTe; and

nanoparticle materials consisting of a first element from any one of the transition metals of the periodic table and a second element from group 16 of the periodic table, and further including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: NiS, CrS, CuInS₂、AgInS₂。

Based on its band gap and lattice constant, ZnSe is a suitable material that meets the criteria for a good shelled material discussed above. Which is a direct bandgap semiconductor with a bandgap of about 2.8eV at 25 c. This corresponds to an absorption onset at about 440nm, so a relatively thick ZnSe crust layer can increase the absorption characteristics of these spots in the desired wavelength region. In some cases, a "thick" skin can be defined as a skin that includes more than one and less than or equal to twenty-two monolayers of material (1 < number of monolayers ≦ 22). In some cases, it is preferred to use a thick housing comprising more than three and less than 22 monolayers of material. In some cases, it is highly preferred to use a thick housing comprising more than three and less than 15 monolayers of material. The lattice constants of InP and ZnSe are respectively

Andwhen epitaxially grown, the lattice strain is about 3.4%, which may inhibit a layer having a greatly increased thickness. If the lattice strain is too high, an alloy of InP-ZnSe or even In can be grown_0.6Ga_0.4A lattice buffer layer composed of a P alloy layer. To electrically and physically isolate the core from the ZnSe layer, additional layers of ZnS and ZnO wide band gap outer shells may be grown.

As an alternative to using a thick ZnSe shell over a simple core/shell type quantum dot (with or without a lattice buffer layer), a quantum dot-quantum well structure may be used. In a quantum dot-quantum well structure, a layer of emissive QD material, such as a layer of CFQD material or a layer of InP material, may be grown around a ZnSe core and then clad (overcoat) with a thick ZnSe layer (1 < number of monolayers ≦ 22, preferably 3 ≦ number of monolayers ≦ 22, or more preferably 3 ≦ number of monolayers ≦ 15). Although the lattice mismatch between material types may still be a problem, it is due to ZnSe_{Inner core}-QD_{Outer casing}And QD_{Outer casing}-ZnSe_{Outer casing}The coherent strain therebetween is eliminated.

A dot-in-rod configuration may also provide the desired increased absorbance and robustness. Here, an emitting QD core, such as a CFQD quantum dot or InP QD core, is embedded in a thick ZnSe shell (1 < monolayer number ≦ 15) that is elongated in one of the x, y, or z planes of the QD core to form a rod. Increased material in the elongated plane may result in increased absorbance compared to a spherical dot. Fig. 4 is a schematic diagram showing a cross-sectional view of a spherical core-shell (CFQD/ZnSe/ZnS) quantum dot configuration, a cross-sectional view of a core-shell (ZnSe/CFQD/ZnSe/ZnS) quantum dot-quantum well configuration, and a cross-sectional view of a quantum dot type configuration within a core-shell (CFQD/ZnSe/ZnS) rod, and schematic illustrations of energy level arrangements of different layers in each configuration.

FIG. 4 (not to scale) shows the relative arrangement of the bandgaps of the different layers in a plurality of nanoparticles according to the invention. In core-shell quantum dots, the CFQD quantum dot core is surrounded by a wider band gap material (ZnSe) which is surrounded by even a wider band gap material (ZnS). The relative band gap energies of the different layers are the same for the rod-in-rod dot type structure. In a quantum dot-quantum well nanoparticle, the ZnSe core is surrounded by a narrower bandgap CFQD quantum dot shell, which is surrounded by a wider bandgap ZnSe shell (having the same band energy as the core) and also a wider bandgap ZnS shell.

The relative position of the band gaps (where the core band gap is completely within the shell band gap) is a typical feature of structures known as "type 1 semiconductor heterostructures" for core-shell and rod-in-rod point type configurations. Conversely, a quantum dot-quantum well configuration will be considered an "inverse type 1 semiconductor heterostructure".

The important features shown in fig. 4 are:

the relative size of the band gap of the material;

the relative energy (position) of the band gaps of the materials with respect to each other.

Compatibility in photoresists

Whether it is core-type QD, core-shell QD, or core-multi-shell QD, the compatibility of a quantum dot with a resin, polymer, or solvent is largely determined by the type of ligand or ligands present on the surface of the quantum dot and the chemical interaction between the ligand and the particular resin, polymer, or solvent. In the case of current indium-based quantum dots, ligand exchange can be difficult because the outer shell can be relatively thin and the effect of the ligand electronically on the inner core dominates. This means that ligand exchange with current materials can be performed during quantum dot synthesis to retain optimal performance. With the incorporation of a thicker ZnSe shell, the core can be better isolated from ligand effects, as described herein, and more conventional ligand exchange strategies can become available.

Propylene glycol monoethylether acetate (PGMEA) is an ideal solvent for color filter applications due to its good wettability, coatability, low toxicity and low boiling point. Currently available cadmium-free quantum dots are typically capped with thiolate and/or carboxylate ligands. It has been found that 6-Mercaptohexanol (MCH) and 2- [2- (2-methoxyethoxy) -ethoxy ] -acetic acid (MEEAA) provide a particularly suitable combination of ligands to impart solubility in PGMEA.

Although MCH and MEEAA have been found to be particularly suitable, other ligands may be used in addition to or as an alternative to MCH and/or MEEAA. For example, in some cases, mercaptoalkyl alcohols or mercaptoalkoxy alcohols, such as, for example, 8-mercapto-1-octanol, 9-mercapto-1-nonanol, 11-mercapto-1-undecanol, 2- {2- [2- (2-mercaptoethoxy) ethoxy ] ethoxy]Ethoxy } ethanol, triethylene glycol mono-11-mercaptoundecyl ether, or (11-mercaptoundecyl) tetra (ethylene glycol). In some cases, thiolated polyethylene glycols (PEGs) such as O- (2-mercaptoethyl) -O' -methyl-hexa (ethylene glycol), H, may be used in some cases₃CO-(CH₂CH₂O)_x-CH₂CH₂SH (X-3-12) or H₃C-(OCH₂CH₂)_x-SH (X ═ 3-24). In some cases, hydroxylated PEG, such as H, can be used₃C-(OCH₂CH₂)_x-OH (X ═ 3-48) or behenyl glycol. In some cases, amine functionalized PEG, such as H, may be used₃C-(OCH₂CH₂)_x-OH (X ═ 2-48). In some cases, carboxylated PEG, such as [2- (2-methoxyethoxy) ethoxy ] ethoxy, may be used]Acetic acid, H₃CO-(CH₂CH₂O)_x-CH₂COOH (X-8-10) or H₃CO-(CH₂CH₂O)_x-CH₂CH₂SH(X＝3-48)。

QDs can be surface functionalized with MCH and MEEAA according to the following general procedure:

first, the QD core is dissolved in a solvent to form a QD solution. The QD concentration of the QD solution may be about 1 milligram (mg) QD/milliliter (mL) of solvent (1mg/mL) to about 500mg/mL, alternatively about 5mg/mL to about 250mg/mL, alternatively about 10mg/mL to about 100mg/mL, and alternatively about 25mg/mL to about 75 mg/mL. To form the shell on the QD core, one or more shell metal precursors are added to the QD-containing solution, followed by MCH. The amount of shell metal precursor and MCH added to the QD-containing solution may vary based on the desired thickness of the shell to be formed on the QD core. In some cases, an excess of one or more of the one or more shell metal precursors and MCH may be added. According to aspects of the present disclosure, from about 0.5ml to about 5ml of MCH may be added to the QD solution per gram of QDs within the QD solution. In some cases, about 1ml to about 4ml of MCH, alternatively about 1.5ml to about 3ml, and alternatively about 1.75ml to about 2.75ml of MCH may be added to the QD solution per gram of QDs within the QD solution. In some cases, all MCH's may be added at once. In some cases, MCH may be added gradually or continuously over a period of time ranging from about 10 minutes to about 6 hours, alternatively from about 15 minutes to about 5 hours, alternatively from about 30 minutes to about 4 hours, and alternatively from about 1 to about 3 hours.

After adding MCH, the solution is heated to a first temperature for a first period of time. The first temperature may be in the range of 180 to 250 ℃ and the first time period may be 10 minutes to 4 hours, for example, a first temperature of 230 ℃ for a time period of about 1 hour. For example, MCH-functionalized coated QDs are isolated by addition of a non-solvent followed by centrifugation.

After isolation, the MCH-functionalized coated QDs (MCH-QDs) are then redispersed in a second solvent and degassed under vacuum to form a solution containing MCH-QDs. The QD concentration of the MCH-QD-containing solution may be from about 1 milligram (mg) MCH-QD/milliliter (mL) of solvent (1mg/mL) to about 500mg/mL, alternatively from about 5mg/mL to about 250mg/mL, alternatively from about 10mg/mL to about 100mg/mL, alternatively from about 15mg/mL to about 50mg/mL, and alternatively from about 20mg/mL to about 40 mg/mL. MEEAA is added and the solution is heated to a second temperature for a second period of time. According to aspects of the present disclosure, about 0.5ml to about 5ml of MEEAA may be added to the MCH-QD-containing solution per gram of MCH-QD within the MCH-QD-containing solution. In some cases, about 1ml to about 4ml of MCH, alternatively about 1.5ml to about 3ml, and alternatively about 1.5ml to about 2.5ml of MEEAA may be added to the QD solution per gram of MCH-QD in the MCH-QD-containing solution. In some cases, an excess of MEEAA may be added. In some cases, the entire MEEAA may be added at once. In some cases, MEEAA may be added stepwise over a period ranging from about 10 seconds to about 10 minutes, alternatively from about 15 seconds to about 5 minutes, alternatively from about 30 seconds to about 3 minutes, and alternatively from about 30 seconds to about 2 minutes. The second temperature may be in the range of 80 to 140 ℃, and the second time period may be about 1 hour to about 24 hours, alternatively about 2 hours to about 20 hours, and alternatively about 4 hours to about 16 hours.

The resulting MCH-and MEEAA-functionalized coated QDs (MCH/MEEAA-QDs) are then separated. In some cases, the resulting MCH/MEEAA-QD was isolated by addition of a non-solvent followed by centrifugation. The resulting MCH/MEEAA-QD was found to be soluble in a wide range of solvents such as toluene, acetone, isopropanol, and PGMEA. Interestingly, MCH/MEEAA-QDs formed according to aspects of the present disclosure were found to be insoluble in extremely non-polar solvents such as hexane as well as extremely polar solvents such as methanol.

The preparation of the QD core may be accomplished in any manner known in the art. As discussed above, CFQD quantum dots can be used as cores in accordance with aspects of the present disclosure. In some cases, methods for making QD cores such as those described in U.S. patent No. 7,588,828 to mustataq et al, entitled "Preparation of nanoparticle materials," which is incorporated herein by reference in its entirety, may be used.

The choice of the metal precursor or precursors may depend on the semiconductor coating desired to be deposited on the QD core. For example, if a ZnS coating is to be provided, the one or more metal precursors can include at least one zinc precursor. Suitable metal precursors include, but are not limited to: carboxylates (e.g., acetates, stearates, myristates, etc.); acetyl pyruvate; halides (e.g., fluoride, chloride, bromide, and iodide); a nitrate salt; and a metal alkyl precursor (e.g., dimethyl zinc or diethyl zinc in the case of a zinc precursor).

The first solvent and the second solvent may be the same or different. In some cases, one or both of the first solvent and the second solvent is a coordinating solvent. Coordinating solvents used in accordance with aspects of the present invention include, but are not limited to: saturated or saturatedUnsaturated C₁-C₂₄Alkyl or aryl alcohols, saturated or unsaturated C₂-C₂₄Alkyl or aryl amines, saturated or unsaturated C₂-C₂₄Alkyl or aryl thiols, saturated or unsaturated C₂-C₂₄Alkyl or aryl selenol, saturated or unsaturated C₁-C₂₄Alkyl or aryl carboxylic acids, phosphines such as trioctylphosphine or phosphine oxides such as trioctylphosphine oxide. In some cases, one or both of the first solvent and the second solvent is a non-coordinating solvent. Examples of suitable non-coordinating solvents include, but are not limited to: linear or branched alkanes having more than 12 carbon atoms, such as dodecane, pentadecane, octadecane, eicosane, triacontane, linear or branched alkenes (e.g., 1-octadecene, 1-eicosene, 1-heptadecene), or heat transfer fluids (e.g.,

66[SOLUTIA INC.，575 MARYVILLE CENTRE DRIVE，ST.LOUIS，MISSOURI 63141]a heat transfer fluid comprising a modified terphenyl). Generally, it is preferred that the non-coordinating solvent, if used, have a boiling point above about 200 ℃ at atmospheric conditions. In a preferred embodiment, the first solvent and the second solvent are non-coordinating solvents.

In an alternative embodiment, the intrinsic QD ligands may be exchanged for carboxylic acid-and thiol-functionalized polyethylene glycol (PEG) ligands, such as MCH and MEEAA, in order to achieve solubility in PGMEA. In some embodiments, a ligand exchange strategy, such as heating the formed QDs in a solution of the desired ligand or ligands to exchange with ligands already disposed on the QD surface.

Liquid crystal display with QD-containing color filter

A prior art Liquid Crystal Display (LCD)500 with a QD-containing backlight unit is schematically shown in fig. 5. The LCD 500 includes a blue light source 501, such as a blue light emitting diode, optically coupled to a Light Guide Plate (LGP) 510. The blue light is transmitted from the LGP510 to the Quantum Dot Film (QDF) 520. The QDF520 has two different types of QDs, one type capable of absorbing blue light from the LGP510 and emitting red light, and the other type capable of absorbing blue light from the LGP510 and emitting green light. The QDF520 is directly above the LGP510 and converts a portion of the blue light from the light source 501 into green and red light, which when mixed with unconverted blue light from the light source 501 produces white light. The white light then travels from the QDF520 and passes through a diffuser film 530, a Brightness Enhancement Film (BEF)540, a Dual Brightness Enhancement Film (DBEF)550, a first reflective polarizer 560, and a Liquid Crystal Layer (LCL)570 in order. After traveling through the LCL 570, the white light is selectively filtered into red, green, and blue colors via red, green, and blue filters 582, 584, 586 of a Color Filter Array (CFA) 580. Thus, the CFA 580 selectively filters the white light to form a single RGB pixel. The red, green, and blue light then travels through a second polarizer 590 to make the user see red 592, green 594, and blue 596. As can be seen, one of the problems with such systems is that a significant portion of the light is filtered out, resulting in a system that is inefficient.

Unlike the use of QD films, QDs can be incorporated directly into the color filters of a color filter array of an LCD, providing a more efficient system and improving the drawbacks of LCD displays such as LCD 500. One way to achieve this is shown in fig. 6. Fig. 6 is a schematic diagram of a Liquid Crystal Display (LCD)600 with QDs directly in the color filters of the color filter array. Unlike the LCD 500, the LCD 600 may achieve color purity by: a desired amount of blue light is emitted from the LCD 600 and substantially 100% of the remaining blue light is converted into red or green light. The LCD 600 includes a blue light source 601, such as a blue light emitting diode, which is optically coupled with a Light Guide Plate (LGP) 610. The blue light exits the LGP 610 and travels through a diffuser film 620, a Brightness Enhancement Film (BEF)630, a Dual Brightness Enhancement Film (DBEF)640, a first reflective polarizer 650, and a Liquid Crystal Layer (LCL)660 and a second reflective polarizer 670 in that order.

Upon exiting second polarizer 670, a portion of the blue light is absorbed by red-converting filter 682 of Color Filter Array (CFA)680, another portion of the blue light is absorbed by green-converting filter 684 of CFA 680, and another portion of the blue light travels through region 686 of CFA 680 that does not contain a color-converting filter. Red-converting filter 682 includes a plurality of quantum dots of a first type dispersed in a suitable matrix material. The first type of quantum dot may be any quantum dot capable of absorbing blue light and emitting red light 692. Green-converting filter 684 includes a plurality of quantum dots of a second type dispersed in a suitable matrix material. The second type of quantum dots can be any quantum dots capable of absorbing blue light and emitting green light 694. The region 686 is made of a suitable matrix material that does not alter the blue light.

The matrix material of red-converting filter 682, green-converting filter 684, and regions 686 may be any suitable photocurable polymer or resin. According to aspects of the present disclosure, a photocurable polymer or resin may be selected that allows at least about 70% transmission of red, green, and blue (RGB) light therethrough. In other cases, the photocurable polymer or resin is selected to allow at least about 80% transmission of RGB light therethrough, at least about 90% transmission of RGB light therethrough, at least about 95% transmission of RGB light therethrough, and at least about 99% transmission of RGB light therethrough.

According to aspects of the present disclosure, the thickness of color-converting filters 682, 684 and region 686 may be in a range of about 5 μm to about 100 μm, alternatively about 5 μm to about 75 μm, alternatively about 5 μm to about 50 μm, alternatively about 10 μm to about 40 μm, and alternatively about 15 μm to about 30 μm. Additionally, according to aspects of the present disclosure, color-converting filters 682, 684 may be made from about 5% to about 80% by weight quantum dots, alternatively from about 5% to about 70% by weight quantum dots, alternatively from about 10% to about 60% by weight quantum dots, and alternatively from about 10% to about 50% by weight quantum dots. In general, as the thickness of the filters 682, 684 increases, the amount of quantum dots dispersed therein may decrease. For example, filters 682, 684 having a thickness of about 15 μm may be made from about 40 wt% to about 60 wt% and alternatively about 50 wt% quantum dots, according to aspects of the present disclosure. Also, for example, filters 682, 684 having a thickness of about 30 μm may be made from about 20 wt% to about 30 wt% and alternatively about 25 wt% quantum dots, according to aspects of the present disclosure. In some cases, one or more of color-converting filters 682, 684 and region 686 may also contain suitable amounts of light scattering agents, such as particles of barium sulfate, titanium dioxide, silicon dioxide, or other similar materials.