CsCu2I3 perovskite thin film with quasi-circular structure and ultraviolet photoelectric detector

Abstract

The invention discloses a CsCu2I3 perovskite thin film with a quasi-circular structure and an ultraviolet photoelectric detector, the CsCu2I3 thin film is composed of quasi-circular crystal grains which are closely stacked, no gap exists between the crystal grains, the crystal grains are uniformly distributed in the whole thin film, the diameter of the crystal grains is 0.01-100 microns, and the thickness of the thin film is 80-2000 nm. Compared with existing nanocrystals and microwires, the thin film has the advantages that the preparation process is simpler, the repetition rate is higher, a thin film sample can more easily meet preparation of large-area and flexible devices, and the thin film has wider application scenes and potential, can be used for electric arc imaging, optical measurement, missile guidance, night vision systems, machine vision, flexible wearable detection equipment and the like, and has wide application prospects. The method has a good application prospect in the fields of image sensing, military supervision, weather monitoring, information communication and the like.

Description

Technical Field

[0001] The invention belongs to the field of optoelectronic devices, and in particular relates to a CsCu2I3 perovskite film with a quasi-circular structure and a photoconductive and photovoltaic ultraviolet photodetector. Background Art

[0002] Photodetectors are a type of photoelectric device that can convert incident photons into electrons, which are then collected by electrodes to form current. They can be widely used in image sensing, optical measurement, missile guidance, night vision systems, machine vision and other fields, and have great application prospects and scientific research value. At present, commercial photodetectors are mainly based on inorganic materials such as Si or GaN. They are characterized by strong stability. Although they have mature technical processes, there are still many problems, such as complex preparation processes, high preparation temperatures, difficulty in preparing large-area flexible devices, high costs, and high driving voltages, which limit the practical application of detectors. In contrast, detectors made of organic materials can be processed by solution, are easy to form films, and can be prepared at low temperature and low cost and on a large area. However, the inherent low carrier mobility, poor transmission performance, and narrow absorption spectrum of organic materials limit the development of photodetectors.

[0003] Perovskite materials (ABX3) are emerging semiconductor materials with many excellent properties, such as direct bandgap materials with adjustable bandgap, high carrier mobility, long carrier diffusion length, high absorption coefficient, absorption band covering ultraviolet to near-infrared band, relatively balanced electron and hole transport performance, etc. In addition, the raw materials of perovskite are abundant and easy to obtain, low-priced, and can be prepared in a simple and mild solution preparation process, low-cost and large-area optoelectronic devices, which has attracted extensive attention from researchers in the field of optoelectronic devices. The use of perovskite, an emerging material, in photodetectors, especially detection in the ultraviolet region, is of great significance for the development of high-performance photodetectors and practical applications. At present, although traditional perovskite materials have been proven to be able to prepare photodetectors, from the perspective of environmental protection, the toxicity of lead in lead halide materials is very unfavorable for its commercialization. Therefore, it is very important to find environmentally friendly lead-free perovskites to prepare photodetectors.

[0004] Lead-free copper-based halide CsCu2I3 is a novel wide bandgap semiconductor material with a bandgap of about 3.62eV. It only absorbs ultraviolet light before 340nm and is an ideal intrinsic material for preparing ultraviolet detectors. Moreover, the material has the advantages of being non-toxic, easy to prepare, high PLQE and high stability, laying a good foundation for the preparation of high-performance ultraviolet photodetectors. Here, the present invention proposes a CsCu2I3 perovskite film with a quasi-circular structure, a photoconductive and photovoltaic ultraviolet photodetector and a preparation method thereof. Summary of the invention

[0005] The purpose of the present invention is to provide a CsCu2I3 perovskite film with a quasi-circular structure and a photoconductive and photovoltaic ultraviolet photodetector. The anti-solvent method is mainly used to prepare a high-quality, large-grain-size CsCu2I3 quasi-circular polycrystalline film, which has an absorption cutoff at 340nm, no absorption of visible light, high PLQY (18.6%), high fluorescence quantum lifetime (136ns), and no self-absorption. The film is spin-coated on a transmission layer substrate or an insulating substrate or a flexible substrate in one step, and then rinsed with an anti-solvent to prepare a CsCu2I3 ultraviolet detector, which can be used for arc imaging, optical measurement, missile guidance, night vision system, machine vision, etc. Compared with existing nanocrystals and micrometer wires, the film of the present invention has a simpler preparation process with a higher repetition rate, and the film sample is more likely to meet the preparation of self-driven photovoltaic structures, large-area and flexible devices, and has a wider range of application scenarios and potentials, and the photoconductive structure detector in the present invention has a higher responsiveness than that of conventional nanocrystals and micrometer wires.

[0006] In order to achieve the above-mentioned invention object, the following technical scheme is adopted:

[0007] A CsCu2I3 perovskite film with a quasi-circular structure, wherein the CsCu2I3 film is composed of closely packed quasi-circular grains, with no gaps between the grains, uniformly distributed in the entire film, with a grain diameter of 0.01-100 μm and a film thickness of 80-2000 nm, preferably a CsCu2I3 perovskite film thickness of 250-300 nm.

[0008] The method for preparing the circular-like CsCu2I3 perovskite film comprises the following steps:

[0009] At room temperature, cesium iodide and cuprous iodide are used as raw materials, and the molar ratio of cesium iodide to cuprous iodide is 0.8-1.2:2.2-1.8, and they are fully dissolved in a solvent to obtain a CsCu2I3 precursor solution. The precursor solution is dropped on a substrate, and a wet film is prepared by a one-step spin coating and an anti-solvent washing assisted crystallization method. The wet film is placed on a hot stage and annealed at 40°C to 180°C for 1min to 60min, and then cooled to room temperature to obtain a CsCu2I3 perovskite thin film layer with a quasi-circular structure.

[0010] The above-mentioned sufficient dissolution method is heating and stirring, and the stirring temperature is preferably 30°C to 100°C.

[0011] Preferably, the molar ratio of cesium iodide to cuprous iodide is 1:2.

[0012] In the method for preparing the circular-like CsCu2I3 perovskite film, the solvent is a mixed solvent of one or more solvents selected from N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and formamide. A mixed solvent of DMF and DMSO in a volume ratio of 1 to 10:1 to 10 is preferred, and a mixed solvent of DMF and DMSO in a volume ratio of 1 to 2:1 to 2 is further preferred.

[0013] The above-mentioned substrate is an insulating substrate or a transmission layer substrate.

[0014] The insulating substrate mentioned above is an insulating hard quartz substrate, a flexible polyethylene terephthalate (PET), or a polyimide (PI) substrate; the transmission layer substrate is one of an epitaxially grown GaN or Ga2O3 substrate.

[0015] The spin coating speed is 2000 to 8000 rpm, and the spin coating time is 10 to 100 seconds.

[0016] The above anti-solvent is any combination of one or more solvents such as toluene, chlorobenzene, p-xylene, benzene bromide, phenol, ether, isopropyl ether, chloroform, methanol, ethanol, ethylene glycol, isopropanol, methyl ethanol, n-butanol, tert-butanol, tetrahydrofuran, dioxane, acetone, cyclohexanone, etc.; the volume ratio of the anti-solvent to the precursor solution is 1:1 to 10:1, and the preferred anti-solvent is toluene. The use of anti-solvent is the key to determining the quality of the film, among which toluene is the best anti-solvent, and a film composed of ultra-large circular grains with a diameter of 0.01-100μm can be obtained, thereby obtaining a device with optimal performance. Moreover, using an anti-solvent to rinse the film during the spin coating process can further improve the crystal quality of the film.

[0017] The above-mentioned photoconductive and photovoltaic ultraviolet photodetector is prepared by using the circular-like structure CsCu2I3 perovskite film, and comprises a CsCu2I3 film, a transmission layer substrate or an insulating substrate, and an electrode.

[0018] The preparation method of the above-mentioned photoconductive and photovoltaic ultraviolet photodetector comprises the following steps:

[0019] 1) Clean the substrate and remove surface impurities;

[0020] 2) Preparing electrodes by magnetron sputtering or vacuum coating;

[0021] 3) using cesium iodide and cuprous iodide as raw materials, and fully dissolving them in a solvent in a molar ratio of cesium iodide: cuprous iodide = 0.8-1.2:2.2-1.8 to prepare a CsCu2I3 precursor solution;

[0022] 4) fixing the electrode prepared in step 2) on a coating machine, absorbing the precursor solution and preparing a thin film on the electrode by a one-step spin coating method. During the spin coating process, the thin film is washed with anti-solvent toluene to form a wet film;

[0023] 5) The prepared wet film is transferred to a hot plate at 40℃~180℃ and annealed for 1min~60min to evaporate the remaining solvent.

[0024] Enhance the crystallization of the film.

[0025] 6) The annealed film is cooled to room temperature to obtain a photoconductive and photovoltaic ultraviolet photodetector.

[0026] The electrode is a patterned semi-transparent or interdigitated electrode of a metal such as Au, Ag, Cu, In, etc. Preferably, the spacing (channel spacing) of the interdigitated electrode is 2 to 1000 μm, the finger length is 0.01 to 100 mm, the finger width is 2 to 100 μm, and the number of interdigitated pairs is 1 to 100 pairs. Further preferably, the electrode is a gold interdigitated electrode, wherein the electrode finger length is 1-5 mm, the finger width is 10-30 μm, the spacing of the interdigitated electrode is 10-30 μm, and the number of interdigitated pairs is 50-60 pairs; preferably, the thickness of the semi-transparent electrode is 15 nm to 900 nm.

[0027] The thin film is covered on the interdigital electrode to form an ohmic contact with gold, and finally a photoconductive ultraviolet detector can be obtained (the thickness is 15nm to 900nm and it can be conductive); the thin film is covered on the transmission layer, and translucent and light-transmitting gold is evaporated on the thin film (the thickness is 15nm to 50nm and it can be light-transmitting and conductive).

[0028] The electrode production is to match the energy levels of patterned Au, Ag, Cu, Cr, In, Al, LiF with one or more conductive metals, and evenly coat them on the surfaces of the thin film layer and the transmission layer as anode and cathode respectively through one or more methods of vacuum coating and magnetron sputtering, with a thickness of 15nm to 900nm.

[0029] The CsCu2I3 thin film of the quasi-circular structure of the present invention covers the surface of the patterned interdigitated electrode on the substrate and forms an ohmic contact with gold, thereby forming a photoconductive structure photodetector.

[0030] Alternatively, a vacuum coating machine is used to coat a layer of translucent Au as an anode on the surface of the transmission layer substrate, and a layer of In as a cathode is coated on the surface of the transmission layer. The circular-shaped CsCu2I3 film forms a heterojunction with GaN, thereby forming a photovoltaic structure ultraviolet photodetector.

[0031] Compared with the prior art, the present invention has the following advantages:

[0032] 1. The present invention uses CsCu2I3 as a semiconductor material, which is more novel, stable, and environmentally friendly than lead-based perovskite, and has good carrier transport capabilities. The film has a wide intrinsic band gap and no absorption of visible light, and can achieve solar-blind ultraviolet detection, thereby showing good responsiveness and sensitivity in the ultraviolet region.

[0033] 2. The CsCu2I3 perovskite film with a circular structure in the present invention has better crystal quality and lower defect state density, and therefore has good optical properties such as high PLQE and high fluorescence quantum lifetime, laying the foundation for high-performance optoelectronic devices.

[0034] 3. The preparation process of the circular-structured CsCu2I3 perovskite film of the present invention adopts a simple low-temperature solution treatment, which does not require complex and expensive material synthesis technology, and the preparation process uses anti-solvent assisted crystallization. The formed polycrystalline film has a special semi-continuous island morphology, which can effectively reduce the dark current of the device, increase the photocurrent of the device, realize the detection of weaker ultraviolet light, and further improve the device performance.

[0035] 4. The ultraviolet photodetector of the present invention contains a photovoltaic structure, which can effectively shorten the carrier migration distance and thus improve the response speed of the device, and the built-in electric field of the heterojunction enables the device to achieve self-driven operation.

[0036] 5. The ultraviolet photodetector of the present invention contains a photoconductive structure, which increases the light absorption area of ​​the perovskite and can maintain a high photocurrent, thereby improving the device responsiveness. Thanks to the good carrier transport capability of the film, the device response time is also greatly shortened.

[0037] 6. Compared with other ultraviolet detection materials, the CsCu2I3 film used in the present invention can be used in the preparation of flexible devices, and the stability is still very good, which is conducive to the future production of flexible sensors. In addition, this non-lead, non-toxic, all-inorganic perovskite has higher commercial value, providing a very feasible solution for the application of perovskite materials in ultraviolet detection.

[0038] 7. The principle of the present invention is simple, meets the current development needs in the field of photoelectric detection, has a wide range of applications, and is easy to promote and apply. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is the structure of the photoconductive ultraviolet photodetector device based on the circular-like structure CsCu2I3 perovskite film in Example 1.

[0040] Figure 2 This is the photovoltaic ultraviolet photodetector device structure based on the circular-like structure CsCu2I3 perovskite film in Example 3.

[0041] Figure 3 This is the XRD spectrum of the CsCu2I3 perovskite film based on the quasi-circular structure on the quartz substrate in Example 1. It can be seen from the figure that the film prepared by the anti-solvent assisted crystallization method has good crystal orientation, does not have any impurity peaks, and can perfectly correspond to the CsCu2I3 standard card, belonging to the orthorhombic phase structure, showing the good crystallinity of the film prepared by this method.

[0042] Figure 4 This is the XRD spectrum of the CsCu2I3 perovskite film based on a quasi-circular structure on a flexible substrate in Example 2. The characteristics are the same as above, but the crystal orientation strength is reduced due to the film formation mechanism problem of the flexible substrate.

[0043] Figure 5 This is the XRD spectrum of the CsCu2I3 perovskite film based on the circular structure on the gallium nitride substrate in Example 3.

[0044] Figure 6 This is a surface SEM image of a CsCu2I3 perovskite film based on a quasi-circular structure on a quartz substrate in Example 1. It can be seen from the figure that the film forms a dense, uniform, hole-free film at a large magnification, and presents a semi-continuous island structure at a small magnification. This structure can effectively reduce the dark current of the device, and the photogenerated carriers can be transmitted at high speed by the densely packed grains, thereby improving the device performance.

[0045] Figure 7 This is a surface SEM image of a CsCu2I3 perovskite film based on a circular-like structure on a flexible substrate in Example 2.

[0046] Figure 8 This is a surface SEM image of a CsCu2I3 perovskite film based on a circular structure on a gallium nitride substrate in Example 3.

[0047] Fig. 9 The CsCu2I3 perovskite film based on the quasi-circular structure in Examples 1-3 has a diameter of 0.01-100 μm and a thickness of 250-300 nm. The crystals grow perpendicular to the substrate and can effectively absorb photons in the ultraviolet region to generate photocurrent.

[0048] Fig.10 This is an optical characterization spectrum of the CsCu2I3 perovskite film based on a quasi-circular structure in Examples 1-3. It can be seen from the figure that the absorption spectrum of the film drops significantly at 325nm, and the absorption cutoff is around 340nm. Under the excitation of ultraviolet light, it shows a bright yellow light emission of 576nm, which represents the common Stokes shift of low-dimensional perovskites. The PLE spectrum is basically consistent with the absorption spectrum, showing the good optical properties and potential ultraviolet detection capabilities of the CsCu2I3 film.

[0049] Fig.11 This is the optical characterization spectrum of the CsCu2I3 perovskite film based on the circular-like structure on the flexible substrate in Example 2.

[0050] Fig.12 This is the optical characterization spectrum of the CsCu2I3 perovskite film based on the circular-like structure on the gallium nitride substrate in Example 3.

[0051] Fig.13 The stability diagram of the CsCu2I3 perovskite film based on the quasi-circular structure in Examples 1-3. It can be seen from the figure that the film is a very stable material in the air environment. After being placed in the ambient air for more than 100 days, the film XRD shows no impurity peaks and obvious degradation, proving that the film still has good crystallinity, which is more stable than traditional lead-based perovskites.

[0052] Fig.14 The current-voltage characteristic curve of the photoconductive ultraviolet detector based on the circular-shaped CsCu2I3 perovskite film in dark conditions in Example 1. It can be seen from the figure that in the dark state, the CsCu2I3 film forms a good ohmic contact with the gold electrode, and the current changes linearly in the voltage range of -20V to 20V.

[0053] Fig.15 The current-voltage characteristic curve of the photoconductive ultraviolet detector based on the circular-shaped CsCu2I3 perovskite film under different light intensities in Example 1. It can be seen from the figure that under the irradiation of ultraviolet light, the device shows obvious photoresponse characteristics, and as the light intensity increases, the photocurrent also increases.

[0054] Fig.16 This is the spectral response curve of the photoconductive ultraviolet detector based on the circular-like structure CsCu2I3 perovskite film in Example 1; it can be seen from the figure that the device only responds to photons in the ultraviolet band, but does not respond to the band after 340nm.

[0055] Fig.17 The curve of the change of current over time at different voltages for the photoconductive ultraviolet detector based on the circular-shaped CsCu2I3 perovskite film in Example 1 is as follows; it can be seen from the figure that the device can maintain good repeatability and good switching characteristics under different bias voltages, and the photocurrent increases significantly with increasing voltage, which can be attributed to the increase in the carrier drift rate due to the enhancement of the electric field, thereby collecting more photogenerated carriers.

[0056] Fig.18The responsivity (R) and specific detectivity (D*) curves of the photoconductive UV detector based on the circular-shaped CsCu2I3 perovskite film in Example 1 under different light intensities are shown in the figure. It can be seen from the figure that the detector has the highest responsivity and specific detectivity under weak light, reaching 8.73A / W and 5.28×10 12 Jones, demonstrated the device’s good weak-light detection and photoelectric conversion capabilities.

[0057] Fig.19 This is the response speed curve of the photoconductive ultraviolet detector based on the circular-structured CsCu2I3 perovskite film in Example 1 under 150Hz modulated light; it can be seen that the rising edge response speed of the device is 1.78ms, and the falling edge response speed is 1.52ms, showing an ultrafast response speed, which is better than the response speed of the currently reported CsCu2I3 thin film devices.

[0058] Fig. 20 The photocurrent curve of the flexible photoconductive ultraviolet detector based on the circular-shaped CsCu2I3 perovskite film in Example 2 as the bending angle changes. It can be seen from the figure that the flexible detector exhibits good switching characteristics. After bending at 30°-120°, the photocurrent of the device hardly changes, showing excellent stability and application potential.

[0059] Fig.21 The light intensity dependence IT curve of the photovoltaic ultraviolet photodetector based on the circular CsCu2I3 perovskite film in Example 3. It can be seen from the figure that the device has good switching characteristics and a high switching ratio under different light intensities, and the light intensity is as low as 2.8μW / cm 2 There is still an obvious on / off ratio under the light intensity.

[0060] Fig. 22 The light intensity-dependent photocurrent curve and responsivity curve of the photovoltaic ultraviolet photodetector based on the circular-shaped CsCu2I3 perovskite film in Example 3. It can be seen from the figure that this photovoltaic device meets the visible-blind ultraviolet spectrum selection and is 2 The low-light response can reach 47.63mA / W.

[0061] Fig.23 The light intensity-dependent normalized detectivity and external quantum efficiency of the photovoltaic ultraviolet photodetector based on the circular-shaped CsCu2I3 perovskite film in Example 3. 2 The maximum detection limit and external quantum efficiency under weak light conditions are as high as 2.58×10 12 Jones and 21.5%.

[0062] Fig.24This is the preparation process of photoconductive ultraviolet detector devices based on circular-structured CsCu2I3 perovskite films.

[0063] Fig.25 The microscope images of CsCu2I3 perovskite films after washing with different anti-solvents in Comparative Example 1. It can be seen that compared with the dendritic structure film after traditional ethyl acetate washing, anti-solvents such as toluene, chlorobenzene, and isopropanol can obtain CsCu2I3 perovskite films with quasi-circular structures, among which the grain size of toluene washing is the largest (10-100μm) and the quality is the best.

[0064] Fig.26 Comparison of the IV curve and response time of the photovoltaic type ultraviolet detector device of the Cu2I3 perovskite film prepared by ethyl acetate and toluene anti-solvent washing in comparative example 2. It can be seen that compared with ethyl acetate washing, the photovoltaic type ultraviolet photodetector prepared by the film after toluene washing has a lower dark current and a faster response speed. DETAILED DESCRIPTION

[0065] The following is a detailed description of an embodiment of the present invention. This embodiment is implemented based on the technical solution of the present invention, and a detailed implementation method and a specific operation process are given in conjunction with the accompanying drawings. However, the protection scope of the present invention is not limited to the following embodiments.

[0066] Example 1

[0067] See also Figure 1 The photoconductive ultraviolet photodetector of this embodiment is a CsCu2I3 polycrystalline thin film with a quasi-circular structure formed on a patterned interdigitated gold electrode by one-step spin coating and anti-solvent assisted crystallization method, and the thin film forms an ohmic contact with the gold electrode, thereby forming a photoconductive structure device operating under a bias voltage. Among them, the CsCu2I3 polycrystalline thin film serves as a light absorption layer and a carrier transmission channel, contributing to the photocurrent.

[0068] The preparation method of the photoconductive ultraviolet photodetector of this embodiment is as follows:

[0069] Step 1. Clean the insulating substrate to remove surface impurities;

[0070] Step 2. Prepare gold interdigital electrodes by magnetron sputtering process, wherein the electrode finger length is 2 mm, the finger width is 20 μm, the channel spacing is 20 μm, and the number of interdigital pairs is 50;

[0071] Step 3. Add 129.9 mg CsI and 190.45 mg CuI into a mixed solvent of 250 μL DMF and 250 μL DMSO, heat to 40°C, and stir for 3 hours to fully dissolve to obtain a CsCu2I3 precursor solution;

[0072] Step 4. Filter the dissolved CsCu2I3 precursor solution using a 0.22 μm filter to filter out unnecessary impurities;

[0073] Step 5. Fix the cleaned interdigital electrode substrate on a coating machine, use a pipette to absorb a certain amount of precursor solution, and use a one-step spin coating method to prepare a thin film on the interdigital electrode, wherein the rotation speed condition is 4000 rpm and the spin coating is 60 seconds;

[0074] Step 6. During the spin coating process, the film was rinsed with anti-solvent toluene, and the volume ratio of anti-solvent to precursor liquid was 10:1 to form a good quality film;

[0075] Step 7. The prepared film was transferred to a hot plate at 100 °C for 10 min for further annealing to evaporate the remaining solvent and enhance the crystallinity of the film;

[0076] Step 8. Cool the annealed film to room temperature to obtain an ultraviolet photodetector based on the CsCu2I3 film.

[0077] Example 2

[0078] In this embodiment, a circular-shaped CsCu2I3 perovskite film is used as the active layer, and flexible insulating polyethylene terephthalate (PET) and polyimide (PI) materials are selected as the substrate to prepare a flexible photodetector that can be bent and folded, thereby providing a possible solution for the application of wearable electronic devices and flexible sensors.

[0079] The method for preparing the flexible photoconductive ultraviolet photodetector in this embodiment is as follows:

[0080] Step 1. Clean the insulating substrate to remove surface impurities. The insulating substrate used is a PET (polyimide) or PET (polyethylene terephthalate) substrate;

[0081] Step 2. Prepare gold interdigital electrodes by magnetron sputtering or vacuum coating, wherein the electrode fingers are 7.5 mm long, 100 μm wide, 50 μm apart, and 15 pairs of interdigital pairs;

[0082] Step 3. Add 0.5 mmol CsI and 1 mmol CuI into a mixed solvent of 250 μl DMF and 250 μl DMSO, heat to 40°C, and stir for 3 hours to fully dissolve to obtain a CsCu2I3 precursor solution;

[0083] Step 4. Filter the dissolved CsCu2I3 precursor solution using a 0.22 μm filter to filter out unnecessary impurities;

[0084] Step 5. Fix the flexible substrate with patterned electrodes on a coating machine, use a pipette to absorb a certain amount of precursor solution, and use a one-step spin coating method to prepare a thin film on the flexible substrate, wherein the rotation speed condition is 4000 rpm and the spin coating is 60 seconds;

[0085] Step 6. During the spin coating process, the film was rinsed with anti-solvent toluene, and the volume ratio of anti-solvent to precursor liquid was 10:1 to form a good quality film;

[0086] Step 7. Transfer the prepared film to a hot plate at 100 °C for 10 min for further annealing to volatilize the remaining solvent and enhance the crystallinity of the film;

[0087] Step 8. Cooling the annealed film to room temperature, thereby obtaining a flexible photoconductive ultraviolet detector based on the CsCu2I3 film;

[0088] Example 3

[0089] See also Figure 2 In this embodiment, an epitaxially grown GaN substrate is selected to be composited with a prepared circular-shaped CsCu2I3 thin film to obtain a high-performance, self-driven photovoltaic ultraviolet photodetector. The CsCu2I3 polycrystalline thin film is used as an active layer, and photogenerated electrons and holes are separated at the interface electric field under light and collected by electrodes to form photocurrent.

[0090] The method for preparing the photovoltaic ultraviolet photodetector in this embodiment is as follows:

[0091] Step 1. Clean the epitaxially grown GaN substrate to remove surface impurities;

[0092] Step 2. Add 129.9 mg CsI and 190.45 mg CuI into a mixed solvent of 250 μL DMF and 250 μL DMSO, heat to 40°C, and stir for 3 hours to fully dissolve to obtain a CsCu2I3 precursor solution;

[0093] Step 3. Filter the dissolved CsCu2I3 precursor solution using a 0.22 μm filter to filter out unnecessary impurities;

[0094] Step 4. Fix the cleaned GaN substrate on a coating machine, use a pipette to absorb a certain amount of precursor solution, and use a one-step spin coating method to prepare a thin film on the interdigital electrode, wherein the rotation speed condition is 4000 rpm and the spin coating is 60 seconds;

[0095] Step 5. During the spin coating process, the film was rinsed with anti-solvent toluene, and the volume ratio of anti-solvent to precursor liquid was 5:1 to form a good quality film;

[0096] Step 6. The prepared film was transferred to a hot plate at 100 °C for 10 min for further annealing to evaporate the remaining solvent and enhance the crystallinity of the film;

[0097] Step 7. Cool the annealed film to room temperature, evaporate a layer of translucent patterned gold electrode on the surface of the film, and evaporate a layer of indium electrode on the surface of GaN, thereby obtaining a photovoltaic ultraviolet photodetector based on a circular-shaped CsCu2I3 film;

[0098] Comparative Example 1

[0099] See also Fig.25 In this example, the morphology of CsCu2I3 films prepared by different types of anti-solvents was compared. The anti-solvents included toluene, ethyl acetate, chlorobenzene, and IPA (isopropyl alcohol). Finally, a CsCu2I3 perovskite film with a quasi-circular structure was obtained under the anti-solvent washing of toluene, chlorobenzene, and isopropyl alcohol. The substrate can be an interdigitated electrode, a transmission layer substrate, or an insulating substrate such as quartz, glass, or flexible.

[0100] The method for preparing the CsCu2I3 thin film in this embodiment is as follows:

[0101] Step 1. Clean any substrate to remove surface impurities;

[0102] Step 2. Add 129.9 mg CsI and 190.45 mg CuI (1:2) into a mixed solvent of 250 μL DMF and 250 μL DMSO, heat to 40°C, and stir for 3 hours to fully dissolve to obtain a CsCu2I3 precursor solution;

[0103] Step 3. Filter the dissolved CsCu2I3 precursor solution using a 0.22 μm filter to filter out unnecessary impurities;

[0104] Step 4. Fix the cleaned substrate on a coating machine, use a pipette to absorb the precursor solution, and use a one-step spin coating method to prepare a thin film on the interdigital electrode, wherein the rotation speed condition is 4000 rpm and the spin coating is 60 seconds;

[0105] Step 5. During the spin coating process, the film was rinsed with toluene, ethyl acetate, chlorobenzene, and IPA (isopropyl alcohol), respectively, with the volume ratio of antisolvent to precursor liquid being 1:1, to form a film of good quality;

[0106] Step 6. The prepared film was transferred to a hot plate at 100 °C for 10 min for further annealing to evaporate the remaining solvent and enhance the crystallinity of the film;

[0107] Step 7. The annealed film is cooled to room temperature and characterized. The film washed with toluene antisolvent has the largest grain size (diameter 0.01-100 μm) and the best quality.

[0108] Comparative Example 2

[0109] See also Fig.26 In this example, a photovoltaic ultraviolet detector prepared by washing with a traditional ethyl acetate anti-solvent and a toluene anti-solvent in this work was compared. Finally, a photovoltaic ultraviolet photodetector based on a circular-shaped CsCu2I3 perovskite film with better performance and faster response was obtained under toluene anti-solvent washing.

[0110] The method for preparing the photovoltaic ultraviolet photodetector in this embodiment is as follows:

[0111] Step 1. Clean the epitaxially grown GaN substrate to remove surface impurities;

[0112] Step 2. Add 129.9 mg CsI and 190.45 mg CuI into a mixed solvent of 250 μL DMF and 250 μL DMSO, heat to 40°C, and stir for 3 hours to fully dissolve to obtain a CsCu2I3 precursor solution;

[0113] Step 3. Filter the dissolved CsCu2I3 precursor solution using a 0.22 μm filter to filter out unnecessary impurities;

[0114] Step 4. Fix the cleaned GaN substrate on a coating machine, use a pipette to absorb a certain amount of precursor solution, and use a one-step spin coating method to prepare a thin film on the interdigital electrode, wherein the rotation speed condition is 4000 rpm and the spin coating is 60 seconds;

[0115] Step 5. During the spin coating process, the film was rinsed with toluene and ethyl acetate antisolvents, respectively, with the antisolvent to precursor liquid volume ratio of 5:1 to form a good quality film;

[0116] Step 6. The prepared film was transferred to a hot plate at 100 °C for 10 min for further annealing to evaporate the remaining solvent and enhance the crystallinity of the film;

[0117] Step 7. Cool the annealed film to room temperature, evaporate a layer of translucent patterned gold electrode on the surface of the film, and evaporate a layer of indium electrode on the surface of GaN, thereby obtaining a photovoltaic ultraviolet photodetector based on a circular-shaped CsCu2I3 film;

[0118] like Fig.26 As shown, compared with the branched film after traditional ethyl acetate washing, the circular structure film obtained by toluene washing can transport carriers faster, improving device performance and response speed.

[0119] The above is only an embodiment of the present invention, and the common knowledge such as the known specific technical schemes or characteristics in the scheme is not described in detail here. The present invention is not limited by the above embodiment, and the above embodiment and description are only preferred examples of the present invention, which are not used to limit the present invention. Any modification, equivalent substitution and deformation improvement made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A CsCu2I3 perovskite film with a quasi-circular structure, characterized in that: The CsCu2I3 film is composed of closely packed circular grains, with no gaps between the grains, which are evenly distributed in the entire film. The diameter of the grains is 0.01-100 μm, and the film thickness is 80-2000 nm.

2. A method for preparing a circular-like CsCu2I3 perovskite film according to claim 1, characterized in that The method comprises the following steps: At room temperature, cesium iodide and cuprous iodide are used as raw materials, and the molar ratio of cesium iodide to cuprous iodide is 0.8-1.2:2.2-1.8, and they are fully dissolved in a solvent to obtain a CsCu2I3 precursor solution. The precursor solution is dropped on a substrate, and a wet film is prepared by a one-step spin coating and an anti-solvent washing assisted crystallization method. The wet film is placed on a hot stage and annealed at 40°C to 180°C for 1min to 60min, and then cooled to room temperature to obtain a CsCu2I3 perovskite thin film layer with a quasi-circular structure.

3. The method for preparing a circular-like structure CsCu2I3 perovskite film according to claim 2, characterized in that: The solvent is a mixture of one or more solvents selected from N,N-dimethylformamide, dimethyl sulfoxide and formamide.

4. The method for preparing a circular-like structure CsCu2I3 perovskite film according to claim 2, characterized in that: The substrate is an insulating substrate or a transmission layer substrate.

5. The method for preparing a circular-like structure CsCu2I3 perovskite film according to claim 2, characterized in that: The spin coating speed is 2000-8000 rpm, and the spin coating time is 10-100 seconds.

6. The method for preparing a circular-like structure CsCu2I3 perovskite film according to claim 4, characterized in that: The insulating substrate is a hard quartz substrate, a flexible polyethylene terephthalate, or a polyimide substrate; the transmission layer substrate is a GaN or Ga2O3 substrate.

7. The method for preparing a circular-like structure CsCu2I3 perovskite film according to claim 2, characterized in that: The anti-solvent is any combination of one or more solvents selected from toluene, chlorobenzene, p-xylene, benzene bromide, phenol, ether, isopropyl ether, chloroform, methanol, ethanol, ethylene glycol, isopropanol, methyl ethanol, n-butanol, tert-butanol, tetrahydrofuran, dioxane, acetone, and cyclohexanone; the volume ratio of the anti-solvent to the precursor solution is 1:1 to 10:1, and the preferred anti-solvent is toluene.

8. An ultraviolet photodetector prepared by using the circular-shaped CsCu2I3 perovskite film prepared by the method of claims 1-7, characterized in that: The ultraviolet photoelectric detector is a photoconductive or photovoltaic ultraviolet photoelectric detector.

9. A method for preparing the ultraviolet photodetector according to claim 8, characterized in that The following steps are involved: 1) Clean the substrate and remove surface impurities; 2) Preparing patterned electrodes by magnetron sputtering or vacuum coating; 3) using cesium iodide and cuprous iodide as raw materials, fully dissolving them in a solvent in a molar ratio of cesium iodide: cuprous iodide = 0.8-1.2:2.2-1.8 to prepare a CsCu2I3 precursor solution; 4) fixing the electrode prepared in step 2) on a coating machine, and applying the precursor solution prepared in step 3) to the electrode by a one-step spin coating method to prepare a thin film. During the spin coating process, the thin film is washed with anti-solvent toluene to prepare a wet film; 5) The prepared wet film is transferred to a hot plate at 40°C to 180°C and annealed for 1 min to 60 min; 6) The annealed film is cooled to room temperature to obtain an ultraviolet photodetector.

10. The method for preparing the ultraviolet photodetector according to claim 9, characterized in that: The electrodes are patterned semi-transparent or interdigitated electrodes of Au, Ag, Cu, or In metal; preferably, the spacing between the interdigitated electrodes is 2 to 1000 μm, the finger length is 0.01 to 100 mm, the finger width is 2 to 100 μm, and the number of interdigitated pairs is 1 to 100 pairs.

Images