Metasurface structure capable of enhancing perovskite light absorption

Abstract

The invention discloses a metasurface structure capable of enhancing perovskite light absorption, and relates to the technical field of micro-nano photonic devices. A cylindrical metasurface unit is directly etched on a perovskite thin film on a silicon substrate, and light reflection is reduced through the resonance effect of the metasurface according to the Mie resonance theory; a layer of metal simple substance is evaporated on the back surface of the silicon substrate through thermal evaporation to serve as a reflecting mirror, and light transmission is reduced by reflecting a light beam through a mirror surface; the structural design successfully realizes the enhancement of the light absorptivity of the perovskite thin film. The structural design is simple, parameters are adjustable, and light absorption enhancement under different wave bands can be achieved; and meanwhile, super-surface processing is directly carried out on the perovskite surface, so that the whole structure is more compact.

Description

Technical Field

[0001] The present invention relates to the technical field of micro-nano photonic devices, and in particular to a super surface structure capable of enhancing light absorption of perovskite. Background Art

[0002] Metasurfaces achieve specific electromagnetic control characteristics by arranging metasurface units on a two-dimensional plane - scatterers or holes at the subwavelength level. Subwavelength structures refer to metasurface units with characteristic dimensions smaller than the target wavelength. Metasurface structures can flexibly control parameters such as the amplitude, phase and polarization of the light field within a wavelength smaller than its structural dimensions. By adjusting the geometric parameters of the unit structure, such as size, shape and direction, the reflected or transmitted wavefront can be arbitrarily controlled, opening up a new path for electromagnetic control. Metasurfaces have the advantages of small size, light weight and easy processing. They have been widely used in various fields of optics, such as micro-nano optical elements, special light field generation, holographic display and imaging, information storage, optical communication, etc. Metasurfaces also have the characteristics of planarization, light weight and easy integration. Polarized light refers to electromagnetic waves with asymmetric vibration direction and propagation direction. At present, polarized light detection relies on a complex optical lens system to distinguish and detect polarized light, while metasurface structures can distinguish and detect polarized light through electromagnetic control. They have a simple structure and are ideal optical structures for polarization detection technology to achieve polarized light detection under the trend of miniaturization and integration. Currently, devices containing metasurface structures are mainly realized by etching optical dielectric materials and metal materials, and the material range of the etching layer has certain limitations.

[0003] Perovskite is a crystalline material with a molecular formula of ABX3 and an octahedral shape. In the perovskite octahedral structure, A is a larger cation, B is a smaller cation, and X is an anion. Each A ion is surrounded by an octahedron formed by B and X ions. Perovskite materials have become promising materials for advanced optoelectronic devices due to their ultra-long carrier diffusion length, low defect and impurity capture incidence, and high carrier mobility. Perovskites have become emerging materials in the form of thin films and colloidal nanocrystals that can be used in high-performance solar cells, light-emitting diodes, lasers, photodetectors, and radiation detectors. However, the integration and miniaturization of advanced optoelectronic devices require reducing the thickness of perovskite materials, resulting in reduced absorption efficiency and external quantum efficiency. This hinders the application of perovskite materials in optoelectronic devices. Therefore, it is necessary to increase the absorption efficiency in the perovskite absorption layer of optoelectronic devices. Summary of the invention

[0004] The problem that the light absorption rate of the current perovskite film is low and difficult to play a role in practical applications. The present invention designs a super surface structure based on the perovskite surface. The structure consists of the top perovskite film, the middle silicon substrate and the bottom metal reflector. The super surface structure is located on the perovskite film layer, and the perovskite film is directly etched by a focused ion beam to obtain a periodically arranged cylindrical super surface unit. In 1908, Gustav Mie obtained a strict solution to elastic scattering of a uniform dielectric sphere by solving the Maxwell equations and proposed the Mie resonance theory. Mie resonance is a structural resonance at microwave frequency. When the scale of the microparticle is close to the microwave wavelength, the microwave and the microparticle will interact with each other, and the interference between the electric and magnetic dipole radiation suppresses the reflection of light without changing the transmission direction of the light. The super surface structure can achieve the enhancement of light absorption on the perovskite surface by making the backscattering zero through the Mie resonance theory. The best light absorption efficiency can be obtained by changing the various parameters of the super surface. The metal reflector part uses the good mirror effect of metal to reflect the light beam transmitted through the substrate, so that the perovskite film can absorb the light for a second time, thereby improving the light absorption efficiency of the perovskite film. Silver has a good mirror effect, and the material is easy to obtain, which is convenient for evaporation operation, so the present invention uses silver as the metal reflector material.

[0005] In order to achieve the above object, the present invention adopts the following technical scheme:

[0006] A super surface structure capable of enhancing perovskite light absorption comprises: the lower surface of a silicon substrate is a metal reflector, the upper surface of the silicon substrate is a perovskite film, and the upper surface of the perovskite film is a super surface structure.

[0007] The thickness of the silicon substrate is in the range of 100nm-1000nm. In order to realize the application in the device, this study selects silicon single crystal commonly used in semiconductor devices as the substrate material; the silicon substrate is obtained by direct purchase.

[0008] The thickness of the perovskite film (including the thickness of the super surface) is 200nm-400nm.

[0009] The super surface structure is a periodic micro-nano structure composed of cylinders with a height of 80nm-130nm and a diameter of 260nm-320nm, and a period of 350nm-450nm.

[0010] The thickness of the metal reflector is 20nm-100nm.

[0011] The method for preparing a super surface structure capable of enhancing perovskite light absorption according to the present invention is characterized in that it comprises the following steps:

[0012] The first step: first, the powders of the components of the perovskite are mixed in proportion, wherein the molar ratio of the cations corresponding to the perovskite structure (one or more selected from inorganic salts, organic salts and chiral organic salts) to the lead halide is 1:1 to 2.5:1, and then an organic solvent (such as DMF, DMSO, etc.) is added, and it is placed on a heating table at 60°C-100°C for stirring to completely dissolve it to form a transparent solution; the transparent solution and the silicon substrate are transferred to an inert gas glove box for spin coating, and the silicon substrate is fixed on a coater, and the coater parameters are preferably set to: speed 1500rpm-3000rpm, time 30s; use a pipette to take an appropriate amount of solution, drop it on the center of the substrate at one time, and then turn on the coater to make the solution evenly distributed on the substrate; the spin-coated substrate is placed on a heating table for annealing, and the organic solvent is evaporated to obtain a flat and dense perovskite film.

[0013] In the second step, a periodic supersurface structure is prepared on the upper surface of the perovskite film. The periodic supersurface structure is etched from the perovskite film. The etching method is: fix the film on a sample plate, put it into a focused ion beam etcher, and bombard it with a Ga ion source according to the drawn pattern to obtain the target pattern.

[0014] The third step is to make the metal adhere to the back of the silicon substrate through thermal evaporation; further fix the substrate on a tray and put it into a thermal evaporator to obtain a uniform and dense metal film.

[0015] It is used to enhance the light absorption in the wavelength range of 300nm-800nm. Since the general response range of perovskite materials is the visible light band, the beam scanning range used in this experiment is 300nm-800nm, and when irradiating, it is perpendicular to the metasurface.

[0016] Beneficial effects of the present invention:

[0017] The present invention simplifies the processing of the entire structure by directly etching a supersurface structure on a perovskite film, thereby eliminating the supersurface layer structure of an optical medium. According to the Mie resonance theory, the resonance effect of the supersurface structure on the perovskite film is used to enhance the light absorption of the perovskite film compared with the structure of only the perovskite film. The light transmission is reduced by using a metal reflector structure, and the light is reflected to the surface of the perovskite film. The above method enhances the light absorption rate of the perovskite film, thereby increasing the possibility of using the perovskite material in optoelectronic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic structural diagram of a perovskite supersurface basic unit provided by an embodiment of the present invention;

[0019] Figure 2The structure of only perovskite film (film), the structure of perovskite film plus metasurface (meta), and the structure of perovskite film plus metasurface plus metal reflector (meta+mirror) provided in the embodiments of the present invention; light transmittance of the bottom surface under 300nm-800nm ​​polarized light irradiation;

[0020] Figure 3 The structure of only perovskite film (film), the structure of perovskite film plus metasurface (meta), and the structure of perovskite film plus metasurface plus metal reflector (meta+mirror) provided in the embodiments of the present invention; the light reflectivity of the bottom surface under 300nm-800nm ​​polarized light irradiation;

[0021] Figure 4 The structure of only perovskite film (film), the structure of perovskite film plus metasurface (meta), and the structure of perovskite film plus metasurface plus metal reflector (meta+mirror) provided in the embodiments of the present invention; light absorption rate of the bottom surface under 300nm-800nm ​​polarized light irradiation; DETAILED DESCRIPTION

[0022] The present invention is further described below with reference to the accompanying drawings and examples, but they are not intended to limit the present invention.

[0023] Example 1

[0024] refer to Figure 1 , a schematic structural diagram of a basic unit of a perovskite supersurface provided by an example of the present invention;

[0025] The structure of the present invention is as follows: a cylindrical perovskite supersurface 1, a perovskite film 2, a silicon substrate 3, and a silver reflector 4. The cylindrical supersurface is obtained by etching the perovskite film to obtain a cylindrical supersurface unit. The height of the supersurface unit cylinder is set to 100nm, the diameter is 280nm, and the period is 400nm; the thickness of the perovskite film is 200nm (including the supersurface thickness of 100nm), the thickness of the silicon substrate is 500nm, and the thickness of the silver reflector is 35nm. The preparation process of the perovskite film: weigh an appropriate amount of chiral organic amine salt R / S-MBAI (methylbenzylamine, R / S is right / left chirality) with a purity of 99.9% and lead halide PbI2 powder medicine, wherein the molar ratio of the chiral organic salt to the lead halide is approximately 1:1, and then the two medicines are mixed, and the mixed powder is put into a dark glass bottle. Use a pipette to absorb an appropriate volume of organic solvent to dissolve the mixed powder medicine, wherein the organic solvent uses DMF. Place the brown glass bottle containing the mixed solution on a heating table with magnetic stirring in a glove box filled with nitrogen atmosphere, set the temperature of the heating table to 60℃, and heat and stir for about 12h to fully dissolve and react the drug. After stirring, in a glove box filled with an inert gas atmosphere, use a pipette to absorb the mixed solution and evenly drip it on the surface of the cleaned silicon substrate. At the same time, turn on the rotation, set the speed to 2000rpm, so that the solution is evenly spread on the substrate. Remove the spin-coated substrate from the rotating table and transfer it to the hot table for annealing. The hot table temperature is set to 90℃ to completely evaporate the organic solvent. Obtain a uniform and dense perovskite film. Etching of cylindrical perovskite supersurface: Use the HeliosG4 PFIB focused ion beam system for etching operation, fix the sample on the sample plate and put it into the instrument, set the etching pattern track for automatic etching. Preparation of silver reflector: Place the silver raw material into the thermal evaporator, set the film thickness, stick the sample to the sample plate with high-temperature tape, and place it into the evaporator for vacuum heating evaporation.

[0026] refer to Figure 2 , a structure of only a perovskite film (film), a structure of a perovskite film plus a metasurface (meta), and a structure of a perovskite film plus a metasurface plus a metal reflector (meta+mirror) provided in an embodiment of the present invention; light transmittance of the bottom surface under 300nm-800nm ​​polarized light irradiation;

[0027] In this example, FDTD simulation shows that when there is only a perovskite film (film) and only a perovskite film metasurface (meta), the light transmittance in the range of 550nm-800nm ​​is higher than 50%, and can reach up to about 90%. After adding a silver reflector, the light transmittance in the entire 300nm-800nm ​​illumination band is reduced to less than 5%, and has been maintained at an extremely low level. The above shows that the silver reflector structure can effectively reduce the transmission of light through the mirror reflection effect, thereby increasing the light absorption rate.

[0028] refer to Figure 3 , the structure of only perovskite film (film), the structure of perovskite film plus metasurface (meta), the structure of perovskite film plus metasurface plus metal reflector (meta+mirror) provided by the examples of the present invention; the light reflectivity of the bottom surface under 300nm-800nm ​​polarized light irradiation;

[0029] In this example, FDTD simulation shows that when there is only a perovskite metasurface (meta), the light reflectivity in the 300nm-800nm ​​band is about 5% lower than when there is only a perovskite film (film), and the light reflectivity is close to 0% at this time, indicating that the perovskite metasurface can suppress the reflection of light, thereby increasing the light absorption rate. After adding a silver reflector (meta+mirror), the reflectivity of the entire structure light increases significantly. This is due to the reflection effect of silver on the transmitted light, so the reflected light beam increases and the light reflectivity increases.

[0030] refer to Figure 4 , the structure of only perovskite film (film), the structure of perovskite film plus metasurface (meta), the structure of perovskite film plus metasurface plus metal reflector (meta+mirror) provided by the examples of the present invention; light absorption rate of the bottom surface under 300nm-800nm ​​polarized light irradiation;

[0031] In this example, FDTD is used for simulation, and the light absorption rate is calculated by the formula A (absorption rate) = 1-T (transmittance) - R (reflectivity); it can be seen from the figure that the metasurface (meta) has a significant enhancement effect on light absorption compared with the film (film) at around 500nm and in the 550nm-650nm band, and the light absorption rate at 550nm is basically 80%, which is increased by about 50%. After adding the silver reflector (meta+mirror), the present invention realizes the enhancement of light absorption rate in the entire 300nm-500nm band, and at the same time, it is correspondingly enhanced a lot in the range of 550nm-680nm, and the light absorption rate at 550nm and 600nm is enhanced by about 50%.

Claims

1. A metasurface structure capable of enhancing light absorption of perovskite, characterized in that: The structure includes: The lower surface of the silicon substrate is a metal reflector, the upper surface of the silicon substrate is a perovskite film, and the upper surface of the perovskite film is a super surface structure.

2. A super surface structure capable of enhancing perovskite light absorption according to claim 1, characterized in that: The silicon substrate has a thickness of 100nm-1000nm, and silicon single crystal is used as the substrate material.

3. A super surface structure capable of enhancing perovskite light absorption according to claim 1, characterized in that: The thickness of the perovskite film (including the thickness of the super surface) is 200nm-400nm.

4. A super surface structure capable of enhancing perovskite light absorption according to claim 1, characterized in that: The super surface structure is a periodic micro-nano structure composed of cylinders with a height of 80nm-130nm and a diameter of 260nm-320nm, and a period of 350nm-450nm.

5. A super surface structure capable of enhancing perovskite light absorption according to claim 1, characterized in that: The thickness of the metal reflector is 20nm-100nm.

6. A method for preparing a super surface structure capable of enhancing perovskite light absorption according to claims 1-5, characterized in that: The following steps are involved: The first step: first, the powders of the components of the perovskite are mixed in proportion, wherein the molar ratio of the cations corresponding to the perovskite structure (one or more selected from inorganic salts, organic salts and chiral organic salts) to the lead halide is 1:1 to 2.5:1, then an organic solvent is added, and the mixture is placed on a heating table at 60°C-100°C for stirring to completely dissolve the mixture to form a transparent solution; the transparent solution and the silicon substrate are transferred to an inert gas glove box for spin coating, and the silicon substrate is fixed on a coater, and the coater parameters are preferably set to: a speed of 1500rpm-3000rpm and a time of 30s; a suitable amount of solution is taken with a pipette and dropped on the center of the substrate at one time, and then the coater is turned on to evenly distribute the solution on the substrate; the spin-coated substrate is placed on a heating table for annealing, and the organic solvent is evaporated to obtain a flat and dense perovskite film; The second step is to prepare a periodic supersurface structure on the upper surface of the perovskite film. The periodic supersurface structure is etched from the perovskite film. The etching method is: fix the film on a sample plate, put it into a focused ion beam etcher, and bombard it with a Ga ion source according to the drawn pattern to obtain the target pattern; The third step is to make the metal adhere to the back of the silicon substrate through thermal evaporation; further fix the substrate on a tray and put it into a thermal evaporator to obtain a uniform and dense metal film.

7. Application of a super surface structure capable of enhancing perovskite light absorption as described in claims 1-5, for enhancing light absorption in the wavelength range of 300nm-800nm.

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