Quantum dot-photonic crystal coupling device and preparation method and application thereof

Abstract

The invention relates to the technical field of quantum dot light emitting diodes, and discloses a quantum dot-photonic crystal coupling device and a preparation method and application thereof, and the method comprises the following steps: preparing a photonic crystal layer on a substrate; depositing a quantum dot film on the photonic crystal layer, and then annealing; sequentially spin-coating a hole transport layer and an electron transport layer on the quantum dot film; and a metal cathode is prepared on the electron transport layer through thermal evaporation, packaging is completed, and the quantum dot-photonic crystal coupling device is obtained. According to the quantum dot-photonic crystal coupling device prepared by the invention, the light extraction efficiency is improved, the color purity is remarkably improved, the stability is greatly improved, the process compatibility is good, the comprehensive performance is optimized, and the application range is expanded.

Description

Technical Field

[0001] The present invention relates to the technical field of quantum dot light-emitting diodes, and in particular to a quantum dot-photonic crystal coupling device and a preparation method and application thereof. Background Art

[0002] Although quantum dot light-emitting diode (QLED) technology has shown great potential in the display field, its practical application is still restricted by several key issues.

[0003] 1. Low light extraction efficiency

[0004] Traditional QLED devices, due to internal total internal reflection (interface total internal reflection) and waveguide effects, trap over 80% of photons inside the device and prevent them from effectively emitting light, resulting in light extraction efficiencies generally below 20%. Existing solutions, such as microlens arrays, suffer from complex manufacturing processes and poor compatibility with thin film structures.

[0005] 2. The problem of insufficient color purity

[0006] Due to the influence of quantum dot size distribution and interface defects, the full width at half maximum (FWHM) of the emission spectrum of existing QLEDs is generally greater than 25nm, which makes it difficult to meet the requirements of high color gamut display.

[0007] 3. Poor environmental stability

[0008] Especially in blue light QLED devices, under high current density working conditions, there are serious ligand shedding and ion migration phenomena, which seriously affect the device life.

[0009] The root causes of these problems are: traditional light extraction enhancement technologies (such as microlens arrays) are difficult to be compatible with the thin film structure of QLED; quantum dot surface ligand engineering fails to effectively solve the stability problem; and existing solutions can often only optimize for a single performance indicator.

[0010] In order to solve the above technical problems, technicians in this field have tried to introduce photonic crystals into QLEDs; however, when trying to introduce photonic crystals, researchers encountered difficulties such as interface energy level mismatch and high-temperature process damage to quantum dots. These problems resulted in the performance improvement of the quantum dot-photonic crystal composite structure being far lower than theoretical expectations. These technical bottlenecks have seriously restricted the commercial application of QLEDs in the field of high-performance displays.

[0011] The main difficulties in solving the above technical problems are:

[0012] 1. How to achieve low-temperature compatibility between photonic crystal structures and QLED device processes;

[0013] 2. How to ensure precise matching of energy levels at the interface between quantum dots and photonic crystals;

[0014] 3. How to maintain device manufacturability while improving performance.

[0015] Therefore, there is an urgent need for a quantum dot-photonic crystal coupling device and its preparation method and application to solve the above technical problems. Summary of the Invention

[0016] The purpose of the present invention is to overcome the existing technical problems and provide a quantum dot-photonic crystal coupling device and its preparation method and application.

[0017] To achieve the above object, the present invention is implemented according to the following technical solutions:

[0018] A method for preparing a quantum dot-photonic crystal coupling device comprises the following steps:

[0019] S1, preparing a photonic crystal layer on a substrate;

[0020] S2, depositing a quantum dot film on the photonic crystal layer, followed by annealing;

[0021] S3, spin coating a hole transport layer and an electron transport layer on the quantum dot film in sequence;

[0022] S4, preparing a metal cathode by thermal evaporation on the electron transport layer, completing the packaging, and obtaining a quantum dot-photonic crystal coupling device.

[0023] Preferably, in step S1, the substrate is ITO glass; and the photonic crystal layer is a TiO2 photonic crystal array with a period of 300 nm.

[0024] Preferably, in step S1, a TiO2 photonic crystal array with a period of 300 nm is prepared on an ITO glass substrate using nanoimprint technology.

[0025] Specifically, in the quantum dot-photonic crystal coupling device of the present invention, the thickness of the substrate is 50-100 μm; the thickness of the photonic crystal layer is 150-500 nm; the thickness of the quantum dot film is 50-150 nm; the thickness of the hole transport layer is 80-120 nm; the thickness of the electron transport layer is 120-180 nm, and the thickness of the metal cathode is 100-200 nm.

[0026] Specifically, step S1 includes the following steps:

[0027] S1.1 Template Preparation

[0028] S1.1.1, Silicon wafer cleaning: Place the silicon wafer in acetone and ethanol and ultrasonically clean for 15 minutes to remove surface oil and impurities, then rinse and dry;

[0029] S1.1.2, Photoresist coating: Place the cleaned silicon wafer in a spin coater and spin-coat the photoresist until the surface of the silicon wafer is evenly covered with the photoresist to a thickness of 100-200 nm. Then, bake the silicon wafer on a hot plate at 180°C for 2 minutes to cure the photoresist.

[0030] S1.1.3, Electron Beam Lithography: Expose the photoresist using an electron beam lithography device according to the designed 300 nm periodic pattern;

[0031] S1.1.4, Development: Place the exposed silicon wafer in a developer, then rinse and dry it to obtain a photoresist template with a pattern.

[0032] S1.1.5, Etching: Place the silicon wafer with the photoresist template in a reactive ion etcher, using CF4 / O2 or CHF3 as etching gas, and etch the silicon wafer to a depth of 500-800 nm to form a silicon template with a 300 nm periodic pattern;

[0033] S1.1.6, Template surface modification: Soak the etched silicon template in a perfluorosilane solution for 1 hour, then remove it and blow dry it with nitrogen to form a layer of release agent on the template surface to facilitate subsequent demolding after imprinting;

[0034] S1.2, Preparation of TiO2 Precursor Solution

[0035] S1.2.1, Solution Preparation:

[0036] At room temperature, butyl titanate was slowly dripped into ethanol while stirring for 30 minutes to fully mix; then acetylacetone and an appropriate amount of benzoin ethyl ether were added and stirred evenly to obtain a TiO2 precursor solution;

[0037] In the TiO2 precursor solution, the volume ratio of butyl titanate, ethanol, and acetylacetone is 20:50:5, and the amount of benzoin ethyl ether used is 1% of the mass of the TiO2 precursor solution;

[0038] S1.2.2, solution filtration: Filter the prepared TiO2 precursor solution through a 0.22 μm filter membrane to remove impurities and particles in the solution;

[0039] S1.3, ITO glass substrate processing

[0040] The ITO glass substrate was ultrasonically cleaned in acetone and ethanol for 15 minutes to remove surface oil and impurities, then rinsed and dried. The cleaned ITO glass substrate was treated in an oxygen plasma treatment machine for 5 minutes to improve the hydrophilicity of the ITO glass substrate surface and facilitate the coating of the TiO2 precursor solution.

[0041] S1.4, Nanoimprint Lithography

[0042] S1.4.1, Precursor solution coating: Place the treated ITO glass substrate in a spin coater and spin-coat the TiO2 precursor solution; after spin coating, bake the ITO glass substrate on an 80°C hot plate for 10 minutes to remove the solvent in the solution and achieve initial gelation of the precursor solution;

[0043] S1.4.2, Imprinting operation: Place the prepared silicon template on the ITO glass substrate coated with TiO2 precursor solution, ensuring close contact between the template and the substrate; Place the sample in the nanoimprint machine, apply a pressure of 50-100 MPa, and heat to 50-80 ° C, maintaining the pressure for 30 seconds; Then turn on the 365nm UV lamp at 50-100mW / cm 2 Irradiate with an intensity of 10-15 minutes to solidify the TiO2 precursor solution;

[0044] S1.4.3, Template peeling: After UV curing is completed, separate the template from the ITO glass substrate to obtain a prototype of a TiO2 photonic crystal array with a 300nm periodic pattern;

[0045] S1.5, annealing treatment

[0046] The imprinted sample was placed in a high-temperature annealing furnace, and the temperature was raised to 450-550°C at a heating rate of 5°C / min and kept warm for 2 hours to allow the TiO2 to form a crystalline structure; after the insulation was completed, it was naturally cooled to room temperature to obtain a substrate with a photonic crystal layer.

[0047] Preferably, in step S2, the quantum dot film is Cs(Na 1 / 5 Bi 1 / 5 Mn 1 / 5 Ni 1 / 5 Zn 1 / 5 )Cl3 quantum dot film; annealing temperature is 80℃.

[0048] Preferably, in step S2, Cs(Na 1 / 5 Bi 1 / 5 Mn 1 / 5 Ni 1 / 5Zn 1 / 5 )Cl3 quantum dot film and annealing treatment was performed at 80℃ in a nitrogen atmosphere to promote the bonding between quantum dots and photonic crystals.

[0049] Specifically, step S2 includes the following steps:

[0050] S2.1, Cs(Na 1 / 5 Bi 1 / 5 Mn 1 / 5 Ni 1 / 5Zn 1 / 5 )Cl3 quantum dot solution preparation

[0051] Cs(Na 1 / 5 Bi 1 / 5 Mn 1 / 5 Ni 1 / 5 Zn 1 / 5 )Cl3 quantum dots were mixed with toluene and then ultrasonically dispersed to prepare Cs(Na 1 / 5 Bi 1 / 5 Mn 1 / 5 Ni 1 / 5 Zn 1 / 5 )Cl3 quantum dot solution;

[0052] S2.2, spin coating deposition of Cs(Na 1 / 5 Bi 1 / 5 Mn 1 / 5 Ni 1 / 5 Zn 1 / 5 )Cl3 quantum dot film

[0053] Cs(Na 1 / 5 Bi 1 / 5 Mn 1 / 5 Ni 1 / 5 Zn 1 / 5 ) Spin-coating the Cl3 quantum dot solution on the surface of the photonic crystal layer; and drying after the spin coating is completed;

[0054] S2.3, annealing

[0055] The sample obtained in step S2.2 was annealed at 80°C for 15-20 min under a nitrogen atmosphere to obtain a Cs(Na 1 / 5 Bi 1 / 5 Mn 1 / 5 Ni 1 / 5 Zn 1 / 5 )Substrate of Cl3 quantum dot film.

[0056] The Cs(Na 1 / 5 Bi 1 / 5 Mn 1 / 5 Ni 1 / 5 Zn 1 / 5 )Cl3 quantum dots are prepared using existing technology. Preferably, in step S3, the material of the hole transport layer is PEDOT:PSS; the material of the electron transport layer is ZnO NPs.

[0057] Specifically, step S3 includes the following steps:

[0058] S3.1, spin coating of hole transport layer PEDOT:PSS (poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid))

[0059] A 1.3–1.7 wt% PEDOT:PSS aqueous solution was spin-coated on

[0060] Cs(Na 1 / 5 Bi 1 / 5 Mn 1 / 5 Ni 1 / 5 Zn 1 / 5 )Cl3 quantum dot film surface; after spin coating, it is dried and then annealed at a temperature of 70-80°C for 10-30 minutes.

[0061] S3.2, spin coating electron transport layer ZnO NPs (nano-zinc oxide)

[0062] ZnO with a particle size of 20-50 nm is mixed with anhydrous ethanol to prepare a ZnO solution with a concentration of 10-20 mg / mL; the ZnO solution is spin-coated on the surface of the hole transport layer; after the spin coating is completed, it is dried and then annealed at a temperature of 80°C for 10-30 minutes.

[0063] Preferably, in step S4, the metal cathode is Ag.

[0064] Specifically, step S4 includes the following steps:

[0065] S4, thermally evaporating a metal cathode Ag on the surface of the hole transport layer to complete device packaging and obtain a quantum dot-photonic crystal coupling device.

[0066] The present invention performs all the fabrication processes except for the photonic crystal layer at low temperatures (no higher than 80°C), ensuring that the quantum dot performance is not damaged by heat. This process is simple and efficient, and has good compatibility with existing QLED production lines.

[0067] The present invention also includes a quantum dot-photonic crystal coupling device prepared by the above preparation method.

[0068] The present invention also includes the application of quantum dot-photonic crystal coupling devices in quantum dot light emitting diodes.

[0069] Specifically, the quantum dot light emitting diodes include rigid quantum dot light emitting diodes, flexible quantum dot light emitting diodes, and transparent quantum dot light emitting diodes.

[0070] The present invention can significantly improve the light output efficiency by designing a specific quantum dot-photonic crystal coupling structure. The present invention utilizes the bandgap regulation characteristics of photonic crystals to achieve selective enhancement and narrowing of the emission spectrum. The present invention can significantly improve the environmental stability of the device through innovative interface bonding technology and protective layer design. The present invention effectively solves the above-mentioned technical problems through specific material selection and structural design without significantly increasing the complexity of the process, thereby increasing the light extraction efficiency of QLED devices to more than 30%, compressing the spectral half-width to within 15nm, and extending the working life to more than 5000 hours, providing a reliable technical solution for the commercial application of QLED.

[0071] Beneficial effects:

[0072] 1. Improved light extraction efficiency: By precisely matching the quantum dot emission spectrum with the photonic crystal band gap, the light extraction efficiency is increased from <20% of traditional QLEDs to >30%, solving the problem of light loss caused by the waveguide effect.

[0073] 2. Significant improvement in color purity: By utilizing the spectral regulation effect of photonic crystals, the emission spectrum half-width (FWHM) is compressed from 25-30nm to below 15nm, and the color gamut coverage is increased to 98% (BT.2020 standard).

[0074] 3. Significantly improved stability: Through quantum dot-photonic crystal interface chemical bonding technology, the device operating life (T95) is extended from 1,000 hours to more than 5,000 hours, especially solving the stability problem of blue light QLED.

[0075] 4. Good process compatibility: It adopts a low-temperature (no more than 80°C) preparation process to avoid damage to quantum dots caused by high temperature. It is compatible with existing QLED production line equipment, greatly reducing the threshold for industrialization.

[0076] 5. Comprehensive performance optimization: Without significantly increasing manufacturing costs, it achieves a coordinated improvement in efficiency, color purity, and stability, solving the problem that traditional technologies can only optimize a single performance indicator.

[0077] 6. Expansion of application scope: The present invention can be applied to rigid, flexible and transparent QLED devices, providing a better solution for emerging application fields such as ultra-high-definition display and flexible electronics. BRIEF DESCRIPTION OF THE DRAWINGS

[0078] Figure 1 This is a process flow chart of Example 1 of the present invention. DETAILED DESCRIPTION

[0079] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0080] There is no particular limitation on the purity of all raw materials in the present invention. The present invention preferably uses industrial purity or conventional purity used in the art.

[0081] The devices used in the present invention are not particularly limited and can be devices commonly used in the art.

[0082] Example 1:

[0083] like Figure 1 As shown, a method for preparing a quantum dot-photonic crystal coupling device includes the following steps:

[0084] Firstly, a TiO2 photonic crystal array with a period of 300 nm was prepared on an ITO glass substrate by nanoimprinting technology; then Cs(Na 1 / 5 Bi 1 / 5 Mn 1 / 5 Ni 1 / 5 Zn 1 / 5 )Cl3 quantum dot film and annealing at 80℃ in a nitrogen atmosphere to promote the bonding of quantum dots to the photonic crystal; then spin-coating the hole transport layer (PEDOT:PSS) and the electron transport layer (ZnO NPs) in sequence; finally, preparing the metal cathode (Ag) by thermal evaporation to complete the device packaging.

[0085] Example 2

[0086] A method for preparing a quantum dot-photonic crystal coupling device comprises the following steps:

[0087] S1.1 Template Preparation

[0088] S1.1.1, Silicon wafer cleaning: Place the silicon wafer in acetone and ethanol and ultrasonically clean for 15 minutes to remove surface oil and impurities, then rinse and dry;

[0089] S1.1.2, Photoresist coating: Place the cleaned silicon wafer in a spin coater and spin-coat the photoresist to evenly cover the surface of the silicon wafer to a thickness of 150 nm. Then, bake the silicon wafer on a hot plate at 180°C for 2 minutes to cure the photoresist.

[0090] S1.1.3, Electron Beam Lithography: Expose the photoresist using an electron beam lithography device according to the designed 300 nm periodic pattern;

[0091] S1.1.4, Development: Place the exposed silicon wafer in a developer, then rinse and dry it to obtain a photoresist template with a pattern.

[0092] S1.1.5, Etching: Place the silicon wafer with the photoresist template in a reactive ion etcher, using CF4 / O2 or CHF3 as the etching gas, and etch the silicon wafer to a depth of 650 nm to form a silicon template with a 300 nm periodic pattern;

[0093] S1.1.6, Template surface modification: Soak the etched silicon template in a perfluorosilane solution for 1 hour, then remove it and blow dry it with nitrogen to form a layer of release agent on the template surface to facilitate subsequent demolding after imprinting;

[0094] S1.2, Preparation of TiO2 Precursor Solution

[0095] S1.2.1, Solution Preparation:

[0096] At room temperature, butyl titanate was slowly dripped into ethanol while stirring for 30 minutes to fully mix; then acetylacetone and an appropriate amount of benzoin ethyl ether were added and stirred evenly to obtain a TiO2 precursor solution;

[0097] In the TiO2 precursor solution, the volume ratio of butyl titanate, ethanol, and acetylacetone is 20:50:5, and the amount of benzoin ethyl ether used is 1% of the mass of the TiO2 precursor solution;

[0098] S1.2.2, solution filtration: Filter the prepared TiO2 precursor solution through a 0.22 μm filter membrane to remove impurities and particles in the solution;

[0099] S1.3, ITO glass substrate processing

[0100] The ITO glass substrate was ultrasonically cleaned in acetone and ethanol for 15 minutes to remove surface oil and impurities, then rinsed and dried. The cleaned ITO glass substrate was treated in an oxygen plasma treatment machine for 5 minutes to improve the hydrophilicity of the ITO glass substrate surface and facilitate the coating of the TiO2 precursor solution.

[0101] S1.4, Nanoimprint Lithography

[0102] S1.4.1, Precursor solution coating: Place the treated ITO glass substrate in a spin coater and spin-coat the TiO2 precursor solution; after spin coating, bake the ITO glass substrate on an 80°C hot plate for 10 minutes to remove the solvent in the solution and achieve initial gelation of the precursor solution;

[0103] S1.4.2, Imprinting operation: Place the prepared silicon template on the ITO glass substrate coated with TiO2 precursor solution, ensuring close contact between the template and the substrate; Place the sample in the nanoimprint machine, apply a pressure of 75 MPa, and heat to 70 ° C, maintaining the pressure for 30 seconds; Then turn on the 365 nm ultraviolet lamp at 75 mW / cm 2 Irradiate with an intensity of 100 nm for 12 min to solidify the TiO2 precursor solution;

[0104] S1.4.3, Template peeling: After UV curing is completed, separate the template from the ITO glass substrate to obtain a prototype of a TiO2 photonic crystal array with a 300nm periodic pattern;

[0105] S1.5, annealing treatment

[0106] The imprinted sample was placed in a high-temperature annealing furnace, and the temperature was raised to 500°C at a heating rate of 5°C / min and kept warm for 2 hours to allow the TiO2 to form a crystalline structure; after the insulation was completed, it was naturally cooled to room temperature to obtain a substrate with a photonic crystal layer.

[0107] S2.1, Cs(Na 1 / 5 Bi 1 / 5 Mn 1 / 5 Ni 1 / 5 Zn 1 / 5 )Cl3 quantum dot solution preparation

[0108] Cs(Na 1 / 5 Bi 1 / 5 Mn 1 / 5 Ni 1 / 5 Zn 1 / 5 )Cl3 quantum dots were mixed with toluene and then ultrasonically dispersed to prepare Cs(Na 1 / 5 Bi 1 / 5 Mn 1 / 5 Ni 1 / 5 Zn 1 / 5 )Cl3 quantum dot solution;

[0109] S2.2, spin coating deposition of Cs(Na 1 / 5 Bi 1 / 5 Mn 1 / 5 Ni 1 / 5 Zn 1 / 5 )Cl3 quantum dot film

[0110] Cs(Na 1 / 5 Bi 1 / 5 Mn 1 / 5 Ni 1 / 5 Zn 1 / 5) Spin-coating the Cl3 quantum dot solution on the surface of the photonic crystal layer; and drying after the spin coating is completed;

[0111] S2.3, annealing

[0112] The sample obtained in step S2.2 was annealed at 80°C for 15 min under a nitrogen atmosphere to obtain a Cs(Na 1 / 5 Bi 1 / 5 Mn 1 / 5 Ni 1 / 5 Zn 1 / 5 )Substrate of Cl3 quantum dot film.

[0113] S3.1, spin coating of hole transport layer PEDOT:PSS (poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid))

[0114] A 1.5 wt% PEDOT:PSS aqueous solution was spin-coated on

[0115] Cs(Na 1 / 5 Bi 1 / 5 Mn 1 / 5 Ni 1 / 5 Zn 1 / 5 )Cl3 quantum dot film surface; after spin coating, it is dried and then annealed at 80℃ for 15min.

[0116] S3.2, spin coating electron transport layer ZnO NPs (nano-zinc oxide)

[0117] ZnO with a particle size of 20-50 nm was mixed with anhydrous ethanol to prepare a ZnO solution with a concentration of 15 mg / mL; the ZnO solution was spin-coated on the surface of the hole transport layer; after the spin coating was completed, it was dried and then annealed at a temperature of 80° C. for 15 minutes.

[0118] S4, thermally evaporating a metal cathode Ag on the surface of the hole transport layer to complete device packaging and obtain a quantum dot-photonic crystal coupling device.

[0119] In this embodiment, the thickness of the ITO glass substrate is 80 μm; the thickness of the TiO2 photonic crystal layer is 200 nm; the thickness of the Cs(Na 1 / 5 Bi 1 / 5 Mn 1 / 5 Ni 1 / 5 Zn 1 / 5 )The thickness of the Cl3 quantum dot film is 55nm; the thickness of the hole transport layer is 90nm; the thickness of the electron transport layer is 180nm, and the thickness of the metal cathode is 135nm.

[0120] The sample prepared in Example 2 was tested and the following data were obtained:

[0121] Example 2 Light extraction efficiency 37％ Emission spectrum full width at half maximum (FWHM) 13nm Color gamut coverage 98.2％ Device operating life (T95) 5008h

[0122] The technical solution of the present invention is not limited to the above-mentioned specific embodiments. Any technical variations made according to the technical solution of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing a quantum dot-photonic crystal coupling device, characterized in that: The following steps are involved: S1, preparing a photonic crystal layer on a substrate; S2, depositing a quantum dot film on the photonic crystal layer, followed by annealing; S3, spin coating a hole transport layer and an electron transport layer on the quantum dot film in sequence; S4, preparing a metal cathode by thermal evaporation on the electron transport layer, completing the packaging, and obtaining a quantum dot-photonic crystal coupling device.

2. The method for preparing a quantum dot-photonic crystal coupling device according to claim 1, wherein: In step S1, the substrate is ITO glass; and the photonic crystal layer is a TiO2 photonic crystal array with a period of 300 nm.

3. The method for preparing a quantum dot-photonic crystal coupling device according to claim 2, wherein: In the step S1, a TiO2 photonic crystal array with a period of 300 nm is prepared on an ITO glass substrate using nanoimprint technology.

4. The method for preparing a quantum dot-photonic crystal coupling device according to claim 1, wherein: In step S2, the quantum dot film is Cs(Na 1 / 5 Bi 1 / 5 Mn 1 / 5 Ni 1 / 5 Zn 1 / 5 )Cl3 quantum dot film; annealing temperature is 80℃.

5. The method for preparing a quantum dot-photonic crystal coupling device according to claim 4, characterized in that: In step S2, Cs(Na 1 / 5 Bi 1 / 5 Mn 1 / 5 Ni 1 / 5 Zn 1 / 5 )Cl3 quantum dot film and annealed at 80℃ in nitrogen atmosphere.

6. The method for preparing a quantum dot-photonic crystal coupling device according to claim 1, wherein: In step S3, the material of the hole transport layer is PEDOT:PSS; The material of the electron transport layer is ZnO NPs.

7. The method for preparing a quantum dot-photonic crystal coupling device according to claim 1, wherein: In step S4, the metal cathode is Ag.

8. A quantum dot-photonic crystal coupling device prepared by the preparation method according to any one of claims 1 to 7.

9. Application of the quantum dot-photonic crystal coupling device according to claim 8 in quantum dot light emitting diodes.

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