An encapsulation structure for enhancing the luminescence performance of nanocrystals and a preparation method thereof

Abstract

The present invention provides a packaging structure for enhancing the luminescence performance of nanocrystals and a preparation method thereof, including a luminescent layer, a resonant cavity, and a packaging layer arranged in sequence from the inside to the outside. The innermost luminescent layer is a nanocrystal, the middle-layer resonant cavity is composed of a plurality of independent metal oxide cavities, and the outermost packaging layer is a transparent polymer. Processing the nano-resonant cavity with nanospheres as an auxiliary chemical template is a flexible, low-cost, and large-scale preparation method. The special structure and periodic pattern endow the material with unique light-matter interaction. By utilizing the flexibility of the resonant cavity design to match the emission peaks of nanocrystals in different bands, based on the Purcell effect, the intrinsic photoluminescence intensity is significantly enhanced. The polymer packaging also effectively improves the stability of the nanocrystals.

Description

Technical Field

[0001] The present invention relates to the field of optoelectronic material preparation, and particularly to a packaging structure for enhancing the luminescence performance of nanocrystals and a preparation method thereof. Background Art

[0002] Display technology has profoundly changed people's lifestyles and is widely regarded as an indispensable part of modern society (Nat. Mater. 2015, 14, 454; Light Sci. Appl. 2018, 7, 17168). Currently, the mainstream display technologies on the market are mainly based on liquid crystal displays (LCDs) and organic light-emitting diode (OLED) displays. Although LCDs are leading in terms of lifespan, cost, resolution density, and peak brightness compared to OLED displays, with the rapidly growing demand for more realistic and low-power-consuming image presentation, the performance of wide color gamut and excellent color reproduction has also been tested (Adv. Mater. 2010, 22, 3076). Currently, traditional commercial display backlights usually rely on blue LEDs and Ce:YAG yellow phosphors, and the yellow spectra they produce are too wide to be converted into highly saturated RGB primary colors (Prog. Mater. Sci. 2016, 84, 59). Alternatively, a combination of green β-Sialon:Eu 2+ and red K2SiF6:Mn 4+ (KSF) phosphors is used. Although the red and green emission spectra are well separated, the green spectrum is quite wide and the red spectrum is not deep enough (Appl. Phys. Express 2009, 2, 022401; Opt. Express 2015, 23, 28707).

[0003] Compared with traditional quantum dot materials such as CdSe and InP, all-inorganic perovskite nanocrystals (PeNCs) (CsPbX3 (X=Cl, Br or I)) are considered to be one of the most promising candidate materials for next-generation backlight displays due to their excellent optical properties (such as color purity and tunable band gap), easy synthesis and high defect tolerance (Chem. Eng. J. 2022, 433, 133195; ACS Energy Lett. 2021, 6, 519; Adv. Funct. Mater. 2022, 32, 2113010). However, the low luminescence efficiency of PeNC films is still a problem that needs to be solved in its commercialization process (Chem. Eng. J. 2020, 393, 124767; Nano Lett. 2018, 18, 1185). Although nanopatterned films can improve their luminescence efficiency, the implementation of the process inevitably relies on technologies such as electron beam lithography (EBL) and focused ion beam (FIB), and faces obstacles in terms of manufacturing area, cost, and processing complexity (Adv. Opt. Mater. 2021, 9, 2001474). In addition, the instability of PeNC films is also a bottleneck for practical applications (Soc. Rev. 2019, 48, 310; Adv. Mater. 2019, 31, 1804294). When PeNC is exposed to the external environment for a long time, various factors such as humidity, light, temperature, and oxygen will lead to the degradation of nanocrystals and severe photoluminescence (PL) quenching (Adv. Funct. Mater. 2021, 31, 2008211). Summary of the invention

[0004] Technical Problem: In view of this, the purpose of the present invention is to provide a packaging structure and a preparation method thereof for enhancing the luminescence performance of nanocrystals. The specific structure and periodic pattern give the material a unique light-matter interaction, which has an important influence on improving the optoelectronic performance of the device. It is worth mentioning that the nanoresonant cavity manufacturing process avoids complex, time-consuming and expensive process flows, laying the foundation for further commercialization outside the laboratory.

[0005] Technical solution: The packaging structure of the present invention for enhancing the luminescence performance of nanocrystals includes a luminescent layer, a resonant cavity and a packaging layer arranged in sequence from the inside to the outside. The innermost luminescent layer is a nanocrystal, the resonant cavity of the middle layer is composed of a number of independent metal oxide cavities, and the outermost packaging layer is a transparent high molecular polymer. When the emission wavelength of the nanocrystal matches the resonant cavity, resonance is formed, and the luminescence of the coupled system is significantly enhanced. The high molecular polymer plays a role in protecting and stabilizing the nanocrystal.

[0006] in,

[0007] The shape of the resonant cavity is hemispherical, conical, inverted pyramid-shaped, polyhedron-shaped or barrel-shaped.

[0008] The nanocrystals are any one or a combination of traditional nanocrystals such as CdS, CdSe, CdTe, ZnSe, InP, InA and perovskite nanocrystals.

[0009] The perovskite nanocrystals are metal halide perovskites with the general formula ABX3, where the A-site cations include MA + (CH3NH3 + )、FA + ([(NH2)2CH] + ) and Cs + ; the B-site is mainly Pb 2+ , or different metal ions Sr 2+ 、Zn 2+ 、Ni 2+ 、Mn 2+ 、Cd 2+ 、Sn 2+ 、Co 2+ 、Eu 3+ 、Er 3+ 、Yb 3+ 、Bi 3+ partially or completely replace Pb 2+ ; X = Cl, Br, I.

[0010] The preparation method of the encapsulation structure for enhancing the luminescence performance of nanocrystals according to the present invention specifically includes the following steps:

[0011] Step 1, assembling a two-dimensional dense nanosphere array on a substrate and performing dry etching treatment;

[0012] Step 2, depositing a metal oxide sol between the etched nanosphere arrays, and forming a nanoscale resonant cavity by removing the nanospheres and crystallizing the metal oxide framework;

[0013] Step 3, coating a mixture of nanocrystals or their precursor solutions and a polymer on the substrate containing the nanoscale resonant cavity, and heating to promote solvent evaporation and nanocrystal growth;

[0014] Step 4, peeling off from the substrate to obtain an independent nanocrystal composite film, i.e., the encapsulation structure for enhancing the luminescence performance of nanocrystals.

[0015] The assembly of the two-dimensional dense nanosphere array is any one of the gravity self-assembly method, Langmuir-Blodgett deposition, spin coating, electrophoresis deposition, vertical deposition method or using a micro-injection MPI system.

[0016] The nanocrystalline composite film has photoluminescence spectra with wavelengths of 400 - 500 nm, 500 - 600 nm, and 600 - 700 nm respectively. Among them,

[0017] When the photoluminescence spectrum of the nanocrystalline composite film is at a wavelength of 400 - 500 nm, the selected nanospheres are: polystyrene spheres with a diameter of 300 - 370 nm and a concentration of 2.5 - 5 wt%.

[0018] When the photoluminescence spectrum of the nanocrystalline composite film is at a wavelength of 500 - 600 nm, the selected nanospheres are: polystyrene spheres with a diameter of 370 - 450 nm and a concentration of 2.5 - 5 wt%.

[0019] When the photoluminescence spectrum of the nanocrystalline composite film is at a wavelength of 600 - 700 nm, the selected nanospheres are: polystyrene spheres with a diameter of 450 - 530 nm and a concentration of 2.5 - 5 wt%.

[0020] For the dry etching treatment, an inductively coupled plasma etcher is selected to complete the etching. The power is selected to be 100 - 150 W, and oxygen and argon are introduced into the inductively coupled plasma etcher, and the gas flow rate is 20 - 50 sccm. Among them,

[0021] When the photoluminescence spectrum of the nanocrystalline composite film is at a wavelength of 400 - 500 nm, the etching time is 5 - 9 s.

[0022] When the photoluminescence spectrum of the nanocrystalline composite film is at a wavelength of 500 - 600 nm, the etching time is 6 - 10 s.

[0023] When the photoluminescence spectrum of the nanocrystalline composite film is at a wavelength of 600 - 700 nm, the etching time is 8 - 12 s.

[0024] The removal of the nanospheres is achieved by dry etching, high-temperature calcination, or dissolution in any one of the solutions of toluene, xylene, chloroform, dichloroethane, acetone, tetrahydrofuran, and ethyl acetate.

[0025] The metal oxide is any one of TiO2, ZnO, VO2, and HfO2. After removing the nanospheres and crystallizing the metal oxide framework, the formed nanocavity will generate resonance peaks with resonance wavelengths of 400 - 500 nm, 500 - 600 nm, and 600 - 700 nm to match the nanocrystals or their precursor solutions with photoluminescence spectra of 400 - 500 nm, 500 - 600 nm, and 600 - 700 nm of the nanocrystalline composite film.

[0026] Advantageous effects: As can be seen from the above, a packaging structure and a preparation method for enhancing the luminescence performance of nanocrystals provided by one or more embodiments of this specification have multiple advantageous effects:

[0027] 1. The problem of too weak resonance of a single nanoresonator can be solved by using an array composed of multiple Mie scatterers, and adjacent resonances will effectively enhance the intensity of the resonance mode. With the increase in the number of scatterers, this enhancement will be further improved. It is worth mentioning that the nanoresonator prepared by adjusting the diameter of the etched nanospheres, the thickness of the metal oxide layer, and the lattice size (i.e., the initial nanosphere diameter) will significantly increase the resonance intensity, thus affecting the transmission spectrum;

[0028] 2. The nanoresonator has the ability to capture, confine, and enhance the light field at the nanoscale. The combination of techniques such as electron beam lithography (EBL) and focused ion beam (FIB) is the most widespread strategy for fabricating nanoresonators. Although these techniques can fabricate high-quality micro / nano structures, when it comes to large-area production, these methods may face bottlenecks in high cost and process design complexity; this method uses a more convenient chemical strategy for processing, overcoming the obstacles in terms of time, cost, and fabrication area for preparing micro / nano structures; the nanoresonator provides an excellent platform for enhancing and tuning the spontaneous emission of nanoscale light sources located nearby, which is crucial for many possible applications of the resonator (such as quantum light sources or displays); the photoluminescence spectrum of the perovskite nanocrystal thin film is strongly reshaped due to the embedding of the nanoresonator, and when the resonator resonance is tuned to the intrinsic emission peak of the perovskite nanocrystals, the emission signal of the coupled system is significantly enhanced;

[0029] 3. The perovskite nanocrystal composite thin film has good stability. The polymer makes the PeNCs separated from each other, hindering further close contact and recombination; in addition, the polymer matrix with tightly packed molecular chains can passivate the perovskite surface and protect it from the environment;

[0030] 4. The perovskite nanocrystal composite thin film has excellent high luminescence and environmental stability, coupled with the characteristics of low cost and large-area fabrication, making it an ideal candidate for the color conversion layer in lighting and display applications; the color gamut of the fabricated LCD backlight module can reach 122% of the National Television Standards Committee (NTSC) standard and 180% of the traditional commercial screen; these results indicate that the perovskite nanocrystal thin film has great potential in optoelectronic applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in one or more embodiments of this specification or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only one or more embodiments of this specification. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0032] Figure 1 Scanning electron microscope image of the nanoresonator;

[0033] Figure 2 Resonance peak of the nanoresonator in Example 2; where h, d, and T represent the thickness of TiO2, the diameter of the etched nanospheres used to prepare the resonator, and the lattice period (initial nanosphere diameter), respectively;

[0034] Figure 3 Comparison of perovskite nanocrystal films with and without embedded nanoresonators. Detailed implementation mode

[0035] To make the objectives, technical solutions, and advantages of the present disclosure clearer and more understandable, the present disclosure will be further described in detail below in conjunction with specific embodiments.

[0036] An encapsulation structure for enhancing the luminescence performance of nanocrystals according to the present invention is successively provided with a light-emitting layer, a resonator, and an encapsulation layer from the inside out. The innermost light-emitting layer is a nanocrystal, the middle resonator is composed of a plurality of independent metal oxide cavities, and the outermost encapsulation layer is a transparent polymer. When the emission wavelength of the nanocrystal matches the resonator, resonance is formed, and the luminescence of the coupling system is significantly enhanced. The polymer plays a role in protecting and stabilizing the nanocrystal. The shape of the resonator is hemispherical, conical, inverted pyramid-shaped, polyhedron-shaped, or barrel-shaped. The nanocrystal is any one or a combination of traditional nanocrystals such as CdS, CdSe, CdTe, ZnSe, InP, InA and perovskite nanocrystals. The perovskite nanocrystal is a metal halide perovskite with the general formula ABX3, where the A-site cation includes MA + (CH3NH3 + ), FA + ([(NH2)2CH] + ) and Cs + ; the B-site is mainly Pb 2+ , or different metal ions Sr 2+ , Zn 2+ , Ni 2+ , Mn 2+ , Cd 2+ , Sn 2+ , Co 2+ , Eu 3+ , Er 3+ , Yb 3+ , Bi 3+ partially or completely replace Pb 2+ ; X = Cl, Br, I.

[0037] Example 1

[0038] This method uses a nanosphere array as an auxiliary template. By filling the gaps between the spheres with a metal oxide sol, the nanosphere auxiliary template is removed while the metal oxide is crystallized at high temperature, thereby obtaining a large-area, low-cost, and easily prepared nanocavity. Finally, a mixture of a perovskite precursor solution and PMMA is coated on the substrate containing the nanocavity, and heating is carried out to promote solvent evaporation and nanocrystal growth to obtain a nanocrystal composite film.

[0039] Step 1: Assembly of a two-dimensional dense nanosphere array.

[0040] Mix a 2.5 wt% colloidal solution of 330 nm polystyrene (PS) nanospheres with ethanol at a volume ratio of 1:1 and sonicate for 30 min - 60 min.

[0041] Based on a micropropulsion injection (MPI) system, the PS nanospheres are directly spread on the water surface at an injection rate of 0.5 mL / h. The solution finally evolves into a monolayer of two-dimensional hexagonal close-packed PS nanospheres at the air / water interface.

[0042] Subsequently, the monolayer of PS nanospheres is transferred to a preset substrate by slowly pumping out water or raising the substrate. The nanospheres are tightly attached to the substrate by self-evaporation or low-temperature baking (below 60 °C).

[0043] Ethanol is added as a dispersant to the water-based PS colloidal solution to reduce the surface tension, so that the PS nanospheres are more effectively dispersed on the water surface. The amount of ethanol additive depends on the size and concentration of the nanospheres.

[0044] By precisely controlling four key parameters in the micropropulsion injection (MPI) system, including the contact state between the injector and the water surface (the nozzle just touches the water surface), the injection speed (0.5 - 6 mL / h), the number of injectors, and the concentration of the PS nanosphere colloidal solution (2.5 - 5 wt%), a large-area PS monolayer with a size exceeding 1 square meter can be easily achieved.

[0045] The substrate can be a quartz wafer, mica sheet, silicon wafer, or flexible material. It is ultrasonically cleaned with deionized water, acetone, and ethanol in sequence for 20 min - 30 min, and after drying, it is treated with an ultraviolet ozone cleaner for 20 min - 30 min to obtain a preset substrate.

[0046] Step 2: Dry etching treatment of the nanosphere array.

[0047] The two-dimensional dense nanosphere array in Step 1 is processed by an inductively coupled plasma etching machine, and a combined gas of oxygen and argon is introduced (power: 100 W; gas flow rate: 50 sccm; time: 9 s) to obtain a nanosphere array after dry etching treatment.

[0048] Step 3: Preparation of TiO2 sol;

[0049] Mix titanium isopropoxide (TTIP, 5 mL), ethanol (45 mL), and acetylacetone (1 mL) as the precursor solution, and stir evenly using a magnetic stirrer (stirring speed set to 800 rpm - 1200 rpm); Next, add hydrochloric acid (0.85 mL) and deionized water (4.5 mL) to the above solution, and stir for 5 h - 8 h to form TiO2 sol;

[0050] Step 4: Fabrication of TiO2-based nanoresonator;

[0051] Take 20 - 50 μL of the TiO2 sol prepared in Step 3, and spin-coat it on the nanoarray etched in Step 2 at a rotational speed of 1000 - 2000 rpm for 30 - 60 s using a spin coater; Then, transfer it to an oven (60 - 75 °C, 12 - 24 h), and calcine it at 480 °C for 2 - 3 h to remove the nanospheres and crystallize the TiO2 framework, forming a TiO2-based nanoresonator;

[0052] To ensure the formation of the nanoresonator structure, the thickness of the TiO2 sol coating should be less than the diameter of the nanospheres treated by dry etching;

[0053] Step 5: Preparation of the CsPbCl 1.5 Br 1.5 perovskite precursor solution and PMMA mixture;

[0054] Obtain a 0.028 mmol / mL perovskite precursor solution by dissolving 0.14 mmol CsCl, 0.14 mmol CsBr, 0.15 mmol PbCl2, and 0.15 mmol PbBr2 in 10 mL of N,N-dimethylformamide (DMF) solvent, and mix it with 1 g of polymethyl methacrylate (PMMA) powder; Among them, stir at a speed of 800 rpm - 1200 rpm for 30 min - 60 min;

[0055] Step 6: Preparation of CsPbCl 1.5 Br 1.5 nanocrystal composite film;

[0056] Coat the mixture of CsPbCl 1.5 Br 1.5 perovskite precursor solution and PMMA prepared in Step 5 on the substrate containing the TiO2-based nanoresonator described in Step 4, and heat it on a hot plate at 80 - 130 °C to promote solvent evaporation and nanocrystal growth. After heating for 2 - 12 min, peel it off from the substrate to form an independent CsPbCl with a photoluminescence spectrum in the wavelength range of 400 - 500 nm1.5 Br 1.5 Nanocrystalline composite thin film

[0057] Preparing a nanoresonator using nanospheres as an auxiliary chemical template is a flexible, low-cost, and large-scale preparation method; the special structure and periodic pattern endow the material with unique light-matter interaction; CsPbCl 1.5 Br 1.5 The photoluminescence (PL) spectrum of the nanocrystalline composite thin film is strongly reshaped due to the embedding of TiO2-based nanoresonators, and the amplitude of resonance-tunable PL enhancement can be changed by varying the nanoresonators in the composite thin film; when the resonator resonance is tuned to the intrinsic emission peak of the nanocrystals, the emission signal of the coupled system is enhanced; at the same time, the spontaneous emission lifetime is shortened, indicating that this enhancement is essentially radiative; PMMA polymer encapsulation also effectively improves the stability of the nanocrystals; it can be widely applied to high-performance perovskite-based optoelectronic devices such as biosensors, light-emitting diodes, and lasers.

[0058] Example 2

[0059] Step 1: Assembly of a two-dimensional dense nanosphere array

[0060] Mix a 2.5 wt% colloidal solution of 390 nm polystyrene (PS) nanospheres with ethanol at a volume ratio of 1:1 and ultrasonicate for 30 min - 60 min; use a micropropulsion injection (MPI) system to directly spread the PS nanospheres on the water surface at an injection rate of 0.5 mL / h; the solution finally evolves into a two-dimensional hexagonal close-packed monolayer of PS nanospheres at the air / water interface; subsequently, transfer the PS nanosphere monolayer to a preset substrate by slowly pumping water or raising the substrate; make the nanospheres adhere tightly to the substrate by self-evaporation or low-temperature baking (below 60 °C);

[0061] Step 2: Dry etching treatment of the nanosphere array

[0062] Treat the two-dimensional dense nanosphere array in step 1 with an inductively coupled plasma etcher, introducing a combined gas of oxygen and argon (power: 100 W; gas flow rate: 50 sccm; time: 10 s) to obtain a dry-etched nanosphere array;

[0063] Step 3: Preparation of TiO2 sol

[0064] Mix titanium isopropoxide (TTIP, 5 mL) with ethanol (45 mL) and acetylacetone (1 mL) as a precursor solution and stir evenly using a magnetic stirrer (stirring speed set to 800 rpm - 1200 rpm); next, add hydrochloric acid (0.85 mL) and deionized water (4.5 mL) to the above solution and stir for 5 h - 8 h to form TiO2 sol;

[0065] Step 4: Fabrication of TiO₂-based nanocavities;

[0066] Take 20 - 50 μL of the TiO₂ sol prepared in Step 3 and spin-coat it on the nanoarray etched in Step 2 using a spin coater at a speed of 1000 - 2000 rpm for 30 - 60 s; then, transfer it to an oven (60 - 75 °C, 12 - 24 h) and calcine it at 480 °C for 2 - 3 h to remove the nanospheres and crystallize the TiO₂ framework, forming TiO₂-based nanocavities;

[0067] Step 5: Preparation of the CsPbBr₃ perovskite precursor solution and PMMA mixture;

[0068] A perovskite precursor solution with a concentration of 0.028 mmol / mL is obtained by dissolving 0.28 mmol CsBr and 0.3 mmol PbBr₂ in 10 mL of N,N-dimethylformamide (DMF) solvent and mixing it with 1 g of polymethyl methacrylate (PMMA) powder; stir it at a speed of 800 - 1200 rpm for 30 - 60 min;

[0069] Step 6: Preparation of CsPbBr₃ nanocrystal composite films using the doctor blade method;

[0070] Coat the mixture of CsPbBr₃ perovskite precursor solution and PMMA in Step 5 on the substrate containing TiO₂-based nanocavities described in Step 4 using a doctor blade coater and heat it on a hot plate at 80 - 130 °C to promote solvent evaporation and nanocrystal growth. After heating for 2 - 12 min, peel it off from the substrate to form a free-standing CsPbBr₃ nanocrystal composite film with a photoluminescence spectrum at a wavelength of 500 - 600 nm;

[0071] Using nanospheres as an auxiliary chemical template to prepare nanocavities is a flexible, low-cost, and large-scale preparation method; the special structure and periodic pattern endow the material with unique light-matter interactions; the photoluminescence (PL) spectrum of the CsPbBr₃ nanocrystal composite film is strongly reshaped due to the embedding of TiO₂-based nanocavities, and the amplitude of the resonance-tunable PL enhancement can be changed by varying the nanocavities in the composite film; when the cavity resonance is tuned to the intrinsic emission peak of the nanocrystals, the emission signal of the coupled system is enhanced; at the same time, the spontaneous emission lifetime is shortened, indicating that this enhancement is essentially radiative; PMMA polymer encapsulation also effectively improves the stability of the nanocrystals; it can be widely applied to high-performance perovskite-based optoelectronic devices such as biosensors, light-emitting diodes, and lasers.

[0072] Example 3

[0073] Step 1: Assembly of two-dimensional dense nanosphere arrays;

[0074] Mix a 2.5 wt% colloidal solution of 470 nm polystyrene (PS) nanospheres with ethanol in a volume ratio of 1:1 and use it after ultrasonic treatment for 30 min - 60 min; Based on the micro - propulsion injection (MPI) system, directly spread the PS nanospheres on the water surface at an injection rate of 0.5 mL / h; The solution finally evolves into a two - dimensional hexagonal close - packed monolayer of PS nanospheres at the air / water interface; Subsequently, transfer the monolayer of PS nanospheres to a preset substrate by slowly pumping water or raising the substrate; Through self - evaporation or low - temperature baking (below 60 °C), make the nanospheres adhere tightly to the substrate;

[0075] Step 2: Dry - etching treatment of the nanosphere array;

[0076] Treat the two - dimensional dense nanosphere array in Step 1 with an inductively coupled plasma etcher, introducing a combined gas of oxygen and argon (power: 100 W; gas flow rate: 50 sccm; time: 12 s) to obtain a dry - etched nanosphere array;

[0077] Step 3: Preparation of TiO₂ sol;

[0078] Mix titanium isopropoxide (TTIP, 5 mL) with ethanol (45 mL) and acetylacetone (1 mL) as the precursor solution and stir it evenly using a magnetic stirrer (stirring speed set to 800 rpm - 1200 rpm); Next, add hydrochloric acid (0.85 mL) and deionized water (4.5 mL) to the above - mentioned solution, and form TiO₂ sol after stirring for 5 h - 8 h;

[0079] Step 4: Processing of TiO₂ - based nanocavities;

[0080] Take 20 - 50 μL of the TiO₂ sol prepared in Step 3 and spin - coat it on the nanometer array etched in Step 2 at a rotation speed of 1000 - 2000 rpm for 30 - 60 s using a spin coater; Then, transfer it to an oven (60 - 75 °C, 12 - 24 h) and calcine it at 480 °C for 2 - 3 h to remove the nanospheres and crystallize the TiO₂ framework, forming TiO₂ - based nanocavities;

[0081] Step 5: Preparation of the mixture of CsPbBrI₂ perovskite precursor solution and PMMA;

[0082] A perovskite precursor solution with a concentration of 0.028 mmol / mL was obtained by dissolving 0.09 mmol CsBr, 0.19 mmol CsI, 0.1 mmol PbBr2, and 0.2 mmol PbI2 in 10 mL of N,N-dimethylformamide (DMF) solvent, and then mixed with 1 g of polymethyl methacrylate (PMMA) powder. Among them, it was stirred at a speed of 800 rpm - 1200 rpm for 30 min - 60 min;

[0083] Step 6: Prepare the CsPbBrI2 nanocrystal composite film by the doctor blade method;

[0084] The mixture of the CsPbBr3 perovskite precursor solution and PMMA in Step 5 was coated on the substrate containing the TiO2-based nanocavity described in Step 4 by a doctor blade coater, and heated on a hot plate at 80 - 130 °C to promote solvent evaporation and nanocrystal growth. After heating for 2 - 12 min, it was peeled off from the substrate to form an independent CsPbBrI2 nanocrystal composite film with a photoluminescence spectrum in the wavelength range of 600 - 700 nm;

[0085] Preparing the nanocavity with nanospheres as an auxiliary chemical template is a flexible, low-cost and large-scale preparation method; the special structure and periodic pattern endow the material with unique light-matter interaction; the photoluminescence (PL) spectrum of the CsPbBrI2 nanocrystal composite film is strongly reshaped due to the embedding of the TiO2-based nanocavity, and the amplitude of the resonance-tunable PL enhancement can be changed by changing the nanocavity in the composite film; when the cavity resonance is tuned to the intrinsic emission peak of the nanocrystals, the emission signal of the coupled system is enhanced; at the same time, the spontaneous emission lifetime is shortened, indicating that this enhancement is essentially radiative; PMMA polymer encapsulation also effectively improves the stability of the nanocrystals; it can be widely applied to high-performance perovskite-based optoelectronic devices such as biosensors, light-emitting diodes and lasers, etc.

[0086] The photoluminescence spectrum was measured by a LabRAM HR Evolution confocal micro-fluorescence spectroscopy system; the morphology and microstructure were observed by a Hitachi Regulus8100 scanning electron microscope (SEM). As a reference, the photoluminescence spectra of perovskite nanocrystal films without embedded nanocavities were measured simultaneously. Obviously, the photoluminescence spectrum of the perovskite nanocrystal film is strongly reshaped due to the embedding of the cavity, and when the cavity resonance is tuned to the intrinsic emission peak of the perovskite nanocrystals, the emission signal of the coupled system is enhanced, among which, CsPbCl 1.5 Br 1.5 The CsPbBr3 and CsPbBrI2 perovskite nanocrystal films increased by 3.54 times, 3.89 times and 3.37 times respectively.

[0087] Overall, the problem of too weak resonance in a single nanoresonator can be solved by using an array composed of multiple Mie scatterers, and adjacent resonances will effectively enhance the intensity of the resonance mode. With the increase in the number of scatterers, this enhancement will be further improved. It is worth mentioning that the nanoresonator prepared by adjusting the diameter of the etched nanospheres, the thickness of the metal oxide layer, and the lattice size (i.e., the initial nanosphere diameter) will significantly increase the resonance intensity, thus affecting the transmission spectrum;

[0088] With the rapid development of micro-nano manufacturing technology, all-dielectric nanophotonic devices have been widely fabricated by combining processes such as electron beam lithography (EBL), reactive ion etching (RIE), and atomic layer deposition; although these technologies can fabricate high-quality micro / nano structures, when it comes to large-scale production, these methods may face bottlenecks in high cost and process design complexity; this method uses a more convenient chemical strategy for processing, overcoming the obstacles in terms of time, cost, and manufacturing area for fabricating micro-nano structures;

[0089] The nanoresonator provides an excellent platform for enhancing and tuning the spontaneous emission of nanoscale light sources located nearby, which is crucial for many possible applications of the resonator (such as quantum light sources or displays); the photoluminescence spectrum of the perovskite nanocrystal film is strongly reshaped due to the embedding of the nanoresonator, and when the resonator resonance is tuned to the intrinsic emission peak of the perovskite nanocrystals, the emission signal of the coupled system is significantly enhanced;

[0090] The perovskite nanocrystal film has good stability, and the polymer makes the PeNCs separated from each other, hindering further close contact and recombination; in addition, the polymer matrix with tight molecular chains can passivate the perovskite surface and protect it from the environment;

[0091] The perovskite nanocrystal film has excellent high luminescence and environmental stability, combined with the characteristics of low cost and large-area manufacturing, making it an ideal candidate for the color conversion layer in lighting and display applications; the color gamut of the fabricated LCD backlight module can reach 122% of the National Television Standards Committee (NTSC) standard and 180% of the traditional commercial screen; these results indicate that the perovskite nanocrystal film has great potential in optoelectronic applications.

[0092] The embodiments of this specification are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of one or more embodiments of this specification shall be included within the protection scope of this disclosure.

Claims

1. A method for preparing a packaging structure for enhancing the luminescence performance of nanocrystals, characterized in that, The preparation method specifically includes the following steps: Step 1, assembling a two-dimensional dense nanosphere array on a substrate and performing dry etching treatment; Step 2, depositing a metal oxide sol between the etched nanosphere arrays, and forming a nanocavity by removing the nanospheres and crystallizing the metal oxide framework; Specific operation: Mix titanium isopropoxide with ethanol and acetylacetone as a precursor solution, and stir evenly using a magnetic stirrer; Next, add hydrochloric acid and deionized water to the above solution, and stir for 5 h - 8 h to form a TiO2 sol; Take the prepared TiO2 sol, spin-coat it on the etched nanoarray through a spin coater, then transfer it to an oven, and calcine it at 480 °C for 2 - 3 h; Step 3, coating a mixture of nanocrystals or their precursor solutions and a polymer on the substrate containing the nanocavity, and heating to promote solvent evaporation and nanocrystal growth; Among them, a perovskite precursor solution is prepared by dissolving one or more of CsCl, CsBr, CsI, PbCl2, PbBr2, and PbI2 in an N,N-dimethylformamide solvent, and mixing it with polymethyl methacrylate powder; Step 4, peeling off from the substrate to obtain an independent nanocrystal composite film, which is a packaging structure for enhancing the luminescence performance of nanocrystals.

2. The preparation method of the encapsulation structure for enhancing the luminescence performance of nanocrystals according to claim 1, characterized in that, The assembly of the two-dimensional dense nanosphere array is any one of the gravity self-assembly method, Langmuir-Blodgett deposition, spin coating, electrophoretic deposition, vertical deposition method, or using a micropropulsion injection MPI system.

3. The preparation method of the encapsulation structure for enhancing the luminescence performance of nanocrystals according to claim 1, characterized in that, For the nanocrystal composite film, its photoluminescence spectrum has wavelengths of 400 - 500 nm, 500 - 600 nm, and 600 - 700 nm respectively. Among them, When the photoluminescence spectrum of the nanocrystal composite film is at a wavelength of 400 - 500 nm, the selected nanospheres are: polystyrene spheres with a diameter of 300 - 370 nm and a concentration of 2.5 - 5 wt%; When the photoluminescence spectrum of the nanocrystal composite film is at a wavelength of 500 - 600 nm, the selected nanospheres are: polystyrene spheres with a diameter of 370 - 450 nm and a concentration of 2.5 - 5 wt%; When the photoluminescence spectrum of the nanocrystal composite film is at a wavelength of 600 - 700 nm, the selected nanospheres are: polystyrene spheres with a diameter of 450 - 530 nm and a concentration of 2.5 - 5 wt%.

4. The preparation method of the encapsulation structure for enhancing the luminescence performance of nanocrystals according to claim 1, characterized in that, For the dry etching treatment, an inductively coupled plasma etcher is selected to complete the etching, with a selected power of 100 - 150 W, and oxygen and argon are introduced into the inductively coupled plasma etcher, and the gas flow rate is 20 - 50 sccm. Among them, When the photoluminescence spectrum of the nanocrystal composite film is at a wavelength of 400 - 500 nm, the etching time is 5 - 9 s, When the photoluminescence spectrum of the nanocrystal composite film is at a wavelength of 500 - 600 nm, the etching time is 6 - 10 s, When the photoluminescence spectrum of the nanocrystal composite film is at a wavelength of 600 - 700 nm, the etching time is 8 - 12 s.

5. The preparation method of the encapsulation structure for enhancing the luminescence performance of nanocrystals according to claim 1, characterized in that The removal of the nanospheres is achieved by dry etching, high-temperature calcination, or dissolution in any one of the solutions of toluene, xylene, chloroform, dichloroethane, acetone, tetrahydrofuran, and ethyl acetate.

6. The preparation method of the encapsulation structure for enhancing the luminescence performance of nanocrystals according to claim 1, characterized in that, The metal oxide is any one of TiO2, ZnO, VO2, and HfO2. After removing the nanospheres and crystallizing the metal oxide framework, the formed nanoresonator will generate resonance peaks with resonance wavelengths of 400 - 500 nm, 500 - 600 nm, and 600 - 700 nm to match the nanocrystals or their precursor solutions with a photoluminescence spectrum of 400 - 500 nm, 500 - 600 nm, and 600 - 700 nm in the nanocrystal composite film.

7. An encapsulation structure for enhancing the luminescence performance of nanocrystals prepared by the preparation method according to claim 1, characterized in that: It includes a light-emitting layer, a resonator, and a packaging layer arranged in sequence. The light-emitting layer is a nanocrystal, the resonator is composed of several independent metal oxide cavities, and the packaging layer is a transparent polymer. When the emission wavelength of the nanocrystal matches the resonator, resonance occurs, and the light emission of the coupling system is significantly enhanced. The polymer plays a role in protecting and stabilizing the nanocrystal.

8. The encapsulation structure for enhancing the luminescence performance of nanocrystals according to claim 7, wherein The shape of the resonator is hemispherical, conical, inverted pyramid-shaped, or barrel-shaped.

9. The encapsulation structure for enhancing the luminescence performance of nanocrystals according to claim 7, wherein The nanocrystal is any one or a combination of traditional nanocrystals such as CdS, CdSe, CdTe, ZnSe, InP, InA, and perovskite nanocrystals.

10. The encapsulation structure for enhancing the luminescence performance of nanocrystals according to claim 9, wherein, The perovskite nanocrystals are metal halide perovskites with the general formula ABX3, where the A-site cations include MA + (CH3NH3 + )、FA + ([(NH2)2CH] + ) and Cs + ; The B site mainly contains Pb 2+ , or different metal ions such as Sr 2+ , Zn 2+ , Ni 2+ , Mn 2+ , Cd 2+ , Sn 2+ , Co 2+ , Eu 3+ , Er 3+ , Yb 3+ , Bi 3+ partially or completely replace Pb 2+ ; X = Cl, Br, I.

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