A method for preparing semiconductor nanosheet white light LED

Abstract

The invention discloses a method for preparing a semiconductor nanosheet-based white light emitting diode (LED), wherein CdSe / CdS core-crown and core-shell nanosheets are used as green and red light emitting layers respectively, and ZnO sol is used as an inorganic ligand to passivate surface defect states of the nanosheets; a nanosheet luminescent film is prepared by a spin coating-high temperature annealing process; finally, a blue light LED is used as a light source to excite a red and green nanosheet composite luminescent film, so as to realize a wide color range nanosheet white light LED device based on the three primary colors of red, green and blue; the application limitations of traditional semiconductor quantum dot materials in the display field can be effectively solved, thereby improving the color saturation of a liquid crystal display backlight source; at the same time, the nanosheet sample is still convenient for preparing the luminescent film by using a solution process combined with a high temperature annealing treatment, and the formed dense, transparent and flat nanosheet luminescent film can isolate the interference of the external environment, and effectively improve the stability of the nanosheet LED device.

Description

Technical Field

[0001] The invention relates to a nanosheet-based white light emitting diode (LED), and in particular to a method for preparing a semiconductor nanosheet white light LED. Background Art

[0002] As a new type of fluorescent material, colloidal semiconductor nanomaterials have shown a variety of superior properties, such as adjustable emission wavelength with size, narrow emission spectrum and temperature-insensitive gain characteristics, and have broad application prospects in the fields of microcavity lasers, lighting and display. Since 2011, the application of semiconductor quantum dots in the field of display technology has made great breakthroughs, using quantum dots to replace traditional YAG:Ce 3+ Yellow phosphor effectively makes up for the disadvantage of traditional white light LEDs that the spectrum of light is not single due to the multi-level structure of phosphors. In addition to the red / green / blue light required for image display, there are other stray lights, which will affect the purity of color reproduction. Since quantum dots have a narrow emission peak (half-height width ~20-40nm), they can achieve a color reproduction display effect with higher color purity. In addition, the light conversion efficiency of quantum dots is relatively high, which can better achieve energy saving and environmental protection. In the field of quantum dot display, the way quantum dot white light LED devices produce white light is usually obtained by blue light LEDs exciting the quantum dot luminescent film coated thereon (red and green quantum dots). At present, with its wide color gamut, high color purity and low energy consumption display performance, companies such as Nanosys, Samsung and TCL have adopted quantum dots with high color saturation for white light LEDs in display backlight components, and display devices based on quantum dot LED backlight components have begun commercial applications and have been favored by the world. In 2017, TCL launched the 65Q960C quantum dot TV product, with a color gamut value of up to 110% of the National Television Standards Committee (NTSC) standard, far exceeding the theoretical maximum value of 100% for organic LED TVs.

[0003] So far, semiconductor quantum dots used in white light LED display devices mainly include II-VI semiconductor quantum dots, I-III-VI semiconductor quantum dots represented by non-toxic CuInS2, and perovskites. The narrower the emission peak, the more realistic the color reproduction, thereby better improving the color gamut of liquid crystal display. Therefore, the pursuit of high color purity and wide color gamut display performance has become the development trend of display backlight sources. However, due to the three-dimensional quantum confinement effect of quantum dots, the internal exciton-phonon coupling leads to a certain broadening of the emission peak of quantum dots, making it difficult to achieve single-frequency spectral emission at a single energy level. The emission peak line width of the above types of quantum dots can only be as narrow as about 20 nm at most.

[0004] At present, the inorganic shell is commonly used to passivate the defect states on the surface of the core nanoluminescent material, and to isolate the direct interference of the surrounding environment (oxygen, moisture, etc.) on the optical properties of quantum dots. However, the disadvantage of the thick shell structure is that it is not conducive to the charge balance injection into the core nanomaterial, which hinders the luminescence efficiency of the electroluminescent LED device to a certain extent. With the increase of shell thickness, the electron wave function in the core will also diffuse to the external thick inorganic shell, and the optical properties of quantum dots are also easily affected by the instability of the surface organic ligands, and the stability of the optical properties of quantum dots is severely challenged. Therefore, in order to overcome the development bottleneck of quantum dot display backlight technology, it is urgent to find a new type of high-quality colloidal semiconductor nanomaterial to realize the application of ultra-wide color gamut white light LED in display backlight. Summary of the invention

[0005] Technical problem: In order to solve the limitations of quantum dots in practical applications in the display field, the present invention proposes an ultra-wide color gamut semiconductor nanosheet-based white light LED that has both excellent optical performance stability and can meet the needs of a new generation of display applications. CdSe / CdS core-crown and core-shell nanosheets are used as green and red light-emitting layers, respectively, and ZnO sol is used as an inorganic ligand to passivate the surface defect states of the nanosheets to improve the optical properties and stability of the nanosheets; a spin coating-high temperature annealing process is used to achieve low-cost and high-efficiency preparation of nanosheet luminescent films, and the high temperature process can remove residual ethanolamine and improve the quality of the nanosheet films; finally, a blue light LED is used as a light source to excite the red and green nanosheet composite luminescent films to achieve a wide color gamut nanosheet white light LED device based on the three primary colors of red, green and blue.

[0006] Technical solution: A method for preparing semiconductor nanosheet white light LED, comprising: using CdSe / CdS core-corona and core-shell nanosheets as green and red light emitting layers respectively, and using ZnO sol as an inorganic ligand to passivate the surface defect states of the nanosheets to obtain CdSe / CdS@ZnO core-corona and core-shell nanosheet solutions, and then using a spin coating-high temperature annealing process to prepare inorganic ZnO sol-modified semiconductor nanosheet films to obtain high-quality red and green nanosheet luminescent films; finally, using a blue light LED chip to excite the red and green nanosheet composite luminescent films to obtain a high-quality sandwich structure nanosheet white light LED device.

[0007] Furthermore, the specific preparation method comprises the following steps:

[0008] (1) Preparation of CdSe / CdS@ZnO core-corona and core-shell nanosheets: The nanosheet core is prepared by colloidal chemistry, and then red and green light emitting core-shell and core-corona heterostructure nanosheets are prepared. The surface ligands of the nanosheets are modified by ZnO inorganic sol to obtain inorganic sol-modified CdSe / CdS@ZnO core-corona and core-shell nanosheet solutions that can respectively emit green and red light.

[0009] (2) Preparation of nanosheet luminescent film by spin coating-high temperature annealing process: First, optimize the thickness of the nanosheet luminescent film to achieve the best luminescent display effect; drip the nanosheet solution onto the substrate, prepare luminescent films of corresponding thickness by setting different spin coating speeds, and then measure the emission spectrum of the film to determine the film thickness; at the same time, explore the preparation of high-quality nanosheet films by controlling the annealing temperature for the nanosheet film annealing process, so as to obtain dense, flat and transparent all-inorganic nanosheet luminescent films with excellent luminescent properties;

[0010] (3) Preparation of nanosheet white light LED devices: Deposit red and green light emitting all-inorganic nanosheet films layer by layer on a quartz substrate to form a nanosheet composite light-emitting layer; Place the red and green nanosheet composite light-emitting layer on the surface of a blue light LED (luminescence wavelength ~450nm), fix and package the two with glue, and use the blue light LED as a light source to excite the red and green nanosheet composite films to obtain a nanosheet white light LED device with wide color gamut display performance; Optimize the nanosheet composite light-emitting layer based on the color gamut measurement results of the nanosheet white light LED, in order to obtain an ultra-wide color gamut white light nanosheet light-emitting device.

[0011] Furthermore, the step (1) of preparing the inorganic sol-modified CdSe / CdS core-corona and core-shell nanosheets specifically includes:

[0012] In the first step, CdSe core nanosheets were prepared by colloidal chemistry, and then red and green light emitting core-shell and core-crown heterostructure nanosheets were prepared;

[0013] Step 2: Surface modification of CdSe / CdS nanosheets: First, the toluene solvent in the CdSe / CdS nanosheet solution obtained above is completely evaporated, centrifuged and purified, and dispersed in a chloroform solution. Then, the obtained nanosheet solution is transferred into a sampling bottle, and an appropriate amount of ethanolamine (1-3 mL) is added, and stirred at room temperature in the dark for 24 hours.

[0014] The third step is inorganic sol ligand modification: Inorganic ZnO sol is prepared by chemical reduction method, and an appropriate amount of ZnO sol 0.1-1 mL is added dropwise to the above-mentioned surface-modified nanosheet sample to implement inorganic ligand modification, and inorganic sol-modified CdSe / CdS@ZnO core-crown and core-shell nanosheet solutions can be obtained respectively.

[0015] Furthermore, in step (2), the nanosheet luminescent film is prepared by a spin coating-high temperature annealing process: the spin coating speed is different between 1000-4000 r; the temperature gradient of the annealing temperature is set at: 200, 250, 300 and 350°C.

[0016] Furthermore, step (3) preparation of nanosheet white light LED device: depositing red and green nanosheet luminescent films layer by layer on the surface of quartz substrate, and repeatedly optimizing the nanosheet composite luminescent layer according to the color gamut measurement results of white light device, refer to step (2); finally, placing the red and green nanosheet composite luminescent film on the surface of blue light LED, and fixing and encapsulating the two by glue.

[0017] Beneficial effects: Compared with pure nanosheet materials, the present invention provides a method for preparing semiconductor nanosheet white light LEDs, which can effectively passivate the surface defects of nanosheets and greatly improve the fluorescence emission performance and stability of nanosheets; the nanosheets also support the preparation of high-quality nanosheet luminescent films in the solution process, effectively reducing the preparation cost and enabling large-scale efficient preparation; based on the design of the nanosheet white light LED device structure, red and green nanosheet films are used as the light-emitting layer, and blue light LEDs are used as the excitation light source to realize an ultra-wide color gamut nanosheet white light LED device based on the three primary colors of red, green and blue, and the color gamut displayed by the nanosheet white light LED can reach more than 140% of the color gamut of the standard display device (NTSC); the prepared semiconductor nanosheet white light LED exhibits excellent wide color gamut display performance and has the potential to be used as a new generation of semiconductor white light devices in commercial display device backlight sources. The preparation method of the present invention is simple and efficient, which is conducive to reducing the device preparation cost and large-scale preparation, thereby promoting the commercial application of colloidal semiconductor nanosheet light-emitting devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the structure of the nanosheet white light LED device in Example 1;

[0019] Figure 2 is a color gamut diagram of the nanosheet white light LED device in Example 1;

[0020] The present invention will be further described below in conjunction with the accompanying drawings.

[0021] like Figure 1-2 As shown, a specific preparation method of a semiconductor nanosheet white light LED comprises the following steps:

[0022] (1) Preparation of CdSe / CdS core-corona and core-shell nanosheets: First, the nanosheet core is prepared by colloidal chemistry, and then red and green light emitting core-shell and core-corona heterostructure nanosheets are prepared, so that the nanosheets still maintain the narrow linewidth emission characteristics and have high nanosheet luminescence efficiency;

[0023] Surface modification of CdSe / CdS nanosheets: The toluene solvent in the CdSe / CdS nanosheet solution obtained above was completely evaporated, centrifuged and purified, and dispersed in a chloroform solution. The obtained nanosheet solution was then transferred to a sampling bottle, 2 mL of ethanolamine was added, and stirred at room temperature in the dark for 24 hours;

[0024] Inorganic sol ligand modification: First, inorganic ZnO sol was prepared by chemical reduction method; then 0.5 mL ZnO sol was added dropwise to the surface-modified nanosheet sample to perform inorganic ligand modification, and inorganic sol-modified CdSe / CdS@ZnO core-corona and core-shell nanosheet solutions were obtained respectively;

[0025] (2) Preparation of nanosheet composite luminescent film by spin coating-high temperature annealing process: The nanosheet solution is dripped onto the substrate, and the spin coating speed is set at 2000 r to prepare the nanosheet luminescent film. The emission spectrum of the film is measured to determine the optimal thickness of the nanosheet film. At the same time, for the nanosheet film annealing process, high-quality nanosheet films are prepared by controlling the annealing temperature at 200, 250, 300 and 350 °C in sequence to obtain a dense, flat and transparent all-inorganic nanosheet composite luminescent layer while maintaining excellent luminescence performance;

[0026] (3) Preparation of nanosheet white light LED devices: Based on the above-mentioned optimized nanosheet film preparation process, all-inorganic nanosheet films emitting red and green light are deposited layer by layer on a quartz substrate to form a nanosheet composite light-emitting layer; the red and green nanosheet composite light-emitting layer is placed on the surface of a blue light LED with a light emission wavelength of ~450 nm, and the two are fixed and packaged by glue; the blue light LED is used as a light source to excite the red and green nanosheet composite films to obtain a nanosheet white light LED device with wide color gamut display performance; the nanosheet composite light-emitting layer is optimized according to the color gamut measurement results of the nanosheet white light LED, in order to obtain an ultra-wide color gamut white light nanosheet light-emitting device.

[0027] Inorganic ligand modification can enhance the optical properties and stability of nanosheets; using blue LED as the light source to excite red and green nanosheet luminescent films can obtain nanosheet white light LED devices with an ultra-wide color gamut; it can effectively solve the application bottleneck of traditional semiconductor quantum dot materials in the display field and can be used as the backlight source of the next generation of liquid crystal display devices with high color saturation.

[0028] The semiconductor nanosheets are green light CdSe / CdS core-crown nanosheets and red light CdSe / CdS core-shell nanosheets modified with zinc oxide sol, which can maintain the optical properties of narrow-band emission of the nanosheets. It is planned to use a blue light LED with a wavelength of ~450 nm as the light source to excite the red and green nanosheet luminescent films, so as to produce a nanosheet white light LED with ultra-wide color gamut display performance.

[0029] The specific preparation method of semiconductor nanosheet white light LED effectively solves the application limitations of traditional semiconductor quantum dot materials in the display field, thereby improving the color saturation of the liquid crystal display backlight source; at the same time, the nanosheet sample is still convenient for preparing the light-emitting film by using a solution process combined with a high-temperature annealing treatment, and the dense, transparent and flat nanosheet light-emitting film formed can isolate the interference of the external environment, effectively improving the stability of the nanosheet LED device. The preparation method of the present invention is simple and efficient, which is conducive to reducing the device preparation cost and mass production, thereby promoting the commercial application of colloidal semiconductor nanosheet light-emitting devices.

[0030] The above description is only a preferred embodiment of the present invention. It should be pointed out that for those skilled in the art, on the premise of following the principles of the present invention, improved experimental schemes should also be regarded as within the protection scope of the present invention.

Claims

1. A method for preparing a semiconductor nanosheet white light LED, characterized in that: include: CdSe core nanosheets are prepared by colloidal chemistry, and after modification, ZnO sol is used as an inorganic ligand to passivate the surface defects of the nanosheets to obtain CdSe / CdS@ZnO core-crown and core-shell nanosheet solutions. Inorganic ZnO sol-modified semiconductor nanosheet films are then prepared by spin coating-high temperature annealing process to obtain high-quality red and green nanosheet luminescent films. Finally, a blue LED chip is used to excite the red and green nanosheet composite luminescent films to obtain high-quality sandwich structure nanosheet white light LED devices. The specific preparation method comprises the following steps: (1) Preparation of CdSe / CdS@ZnO core / crown and core / shell nanosheets: The nanosheet core is prepared by colloidal chemistry, and then red and green light emitting core / shell and core / crown heterostructure nanosheets are prepared. After modification, the nanosheets are surface-ligand modified by ZnO inorganic sol to obtain inorganic sol-modified CdSe / CdS@ZnO core / crown and core / shell nanosheet solutions that can respectively emit green and red light. The specific preparation of the inorganic sol-modified CdSe / CdS core-corona and core-shell nanosheets in step (1) includes: In the first step, CdSe core nanosheets were prepared by colloidal chemistry, and then red and green light emitting core-shell and core-crown heterostructure nanosheets were prepared; Step 2: Surface modification of CdSe / CdS nanosheets: First, the toluene solvent in the CdSe / CdS nanosheet solution was completely evaporated, centrifuged and purified, and dispersed in a chloroform solution. Then, the obtained nanosheet solution was transferred into a sampling bottle, ethanolamine was added, and stirred at room temperature in the dark for 24 hours. The third step is inorganic sol ligand modification: Inorganic ZnO sol is prepared by chemical reduction method, and the ZnO sol is added dropwise to the surface-modified nanosheet sample to perform inorganic ligand modification, thereby obtaining inorganic sol-modified CdSe / CdS@ZnO core-corona and core-shell nanosheet solutions respectively; (2) Preparation of nanosheet luminescent film by spin coating-high temperature annealing process: First, optimize the thickness of the nanosheet luminescent film, drip the nanosheet solution onto the substrate, prepare luminescent films of corresponding thickness by setting different spin coating speeds, and then measure the emission spectrum of the film to determine the film thickness; at the same time, explore the preparation of high-quality nanosheet films by controlling the annealing temperature for the nanosheet film annealing process, so as to obtain a dense, flat and transparent all-inorganic nanosheet luminescent film; (3) Preparation of nanosheet white light LED devices: deposit red and green light emitting all-inorganic nanosheet films layer by layer on a quartz substrate to form a nanosheet composite light-emitting layer; place the red and green nanosheet composite light-emitting layer on the surface of a blue light LED, fix and package the two with glue, and use the blue light LED as a light source to excite the red and green nanosheet composite films to obtain a nanosheet white light LED device with wide color gamut display performance; optimize the nanosheet composite light-emitting layer based on the color gamut measurement results of the nanosheet white light LED, in order to obtain an ultra-wide color gamut white light nanosheet light-emitting device.

2. The method for preparing a semiconductor nanosheet white light LED according to claim 1, characterized in that: Step (2) spin coating-high temperature annealing process is used to prepare the nanosheet luminescent film: different spin coating speeds are between 1000-4000r; the temperature gradient of the annealing temperature is set at: 200°C, 250°C, 300°C and 350°C.

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