Preparation method of lead-tin mixed perovskite single crystal thin film and near-infrared detection application thereof

Abstract

The application discloses a preparation method of a lead-tin mixed perovskite single crystal thin film and near-infrared detection application thereof, and relates to the technical field of photoelectric materials and devices. The method introduces an anti-solvent into a saturated precursor liquid to prepare a high-quality seed layer, and dynamically supplements a growth liquid in a key stage of space-limited growth, effectively solves a crystal boundary pore problem caused by solute depletion, and successfully prepares a dense, pore-free and continuous lead-tin mixed perovskite single crystal thin film. Further combined with precursor liquid concentration optimization, an ammonium thiocyanate additive and Me-4PACz interface modification, the defect state density of the thin film is significantly reduced.

Description

Technical Field

[0001] This invention relates to the field of optoelectronic materials and devices, specifically to a method for preparing a lead-tin mixed perovskite single-crystal thin film and its near-infrared detection application. Background Technology

[0002] With the rapid development of next-generation information technologies such as the Internet of Things and artificial intelligence, the demand for high-performance optoelectronic sensing technology in cutting-edge fields such as autonomous driving (LiDAR), biomedicine (health monitoring), and security surveillance is experiencing explosive growth. These applications typically operate in the near-infrared band of 850-1000 nm, placing extremely high demands on the sensitivity and response speed of detectors. However, currently commercially available mainstream near-infrared detectors still face many limitations: traditional silicon-based detectors are limited by their indirect bandgap characteristics, resulting in a low absorption coefficient in this band; while III-V semiconductor detectors such as indium gallium arsenide (InGaAs) have excellent performance, their fabrication relies on expensive vacuum epitaxy equipment, making the process complex and costly, which is difficult to meet the future demand for low-cost, large-area, and flexible applications.

[0003] Metal halide perovskite materials offer a highly competitive option for novel high-performance photodetectors due to their excellent photoelectric properties and low-temperature solution processing capabilities. In particular, lead-tin (Pb-Sn) mixed perovskites, through compositional tuning, can achieve an ideal narrow bandgap of approximately 1.25 eV, with a spectral response range covering the critical near-infrared window. However, Sn in lead-tin perovskites... 2+ The rapid oxidation and crystallization rate of polycrystalline thin films inevitably result in numerous defects such as grain boundaries and pinholes in polycrystalline films prepared using traditional solution methods. These defects, acting as non-radiative recombination centers and leakage channels, significantly increase the dark current and noise of the device, severely limiting the improvement of detector sensitivity and stability.

[0004] To overcome the defect bottleneck of polycrystalline thin films, fabricating grain boundary-free, low-defect perovskite single-crystal thin films is an ideal solution. However, the fabrication of lead-tin mixed perovskite single-crystal thin films currently faces significant challenges: due to the extreme difficulty in controlling the crystallization kinetics of the lead-tin system, conventional crystal growth methods struggle to maintain a stable solute supply during prolonged high-temperature growth. Growth often stalls due to solvent evaporation and elemental depletion, leaving incompletely fused pores in the final film, making it difficult to obtain dense, large-area single-crystal thin films. Therefore, addressing the technical bottlenecks of numerous defects in polycrystalline thin films and the difficulty in achieving film formation with existing single-crystal growth processes, there is an urgent need to develop a novel growth process that can continuously provide growth driving force during the growth process to achieve the fabrication of high-performance self-driven near-infrared detectors. Summary of the Invention

[0005] To address the shortcomings of the aforementioned background technologies, this invention primarily targets the problems of numerous grain boundary defects, limited carrier transport, and porosity and discontinuities easily generated during large-area film formation using traditional single-crystal growth methods in existing lead-tin mixed perovskite polycrystalline thin films. This invention provides a method for preparing lead-tin mixed perovskite single-crystal thin films and their near-infrared detection applications. This method, through the introduction of antisolvent-assisted induced nucleation and a unique secondary crystal growth strategy, combined with additive engineering and interface modification, achieves the controllable preparation of high-quality, dense, porosity-free, and continuous lead-tin mixed perovskite single-crystal thin films, and based on this, constructs a highly sensitive self-driven near-infrared detector.

[0006] The first objective of this invention is to provide a method for preparing a lead-tin mixed perovskite single-crystal thin film, comprising the following steps: Preparation of a saturated precursor solution of lead-tin mixed perovskite; Adding an antisolvent to a saturated precursor solution yields a suspension; The suspension was dropped onto a functionalized substrate, and a uniformly distributed lead-tin mixed perovskite seed layer was formed on the surface of the functionalized substrate by spin coating and annealing. After adding growth solution to a lead-tin mixed perovskite seed layer, a confined space is formed on the seed layer by covering it with a cover plate. Pressure is then applied to the cover plate, and crystal growth is performed by programmed temperature increase. During the temperature increase, growth solution is added to the confined space to induce secondary crystal growth. After the growth is completed, the pressure and cover plate are removed, and the crystal is allowed to cool naturally to room temperature, thus obtaining a lead-tin mixed perovskite single crystal thin film on a functionalized substrate. The growth solution is the clear supernatant of a saturated precursor solution of lead-tin mixed perovskite. The programmed temperature rise is as follows: first, rapidly raise the temperature to 50~65℃ at a rate of 25-30℃ / h, then raise the temperature to 85~95℃ at a rate of 0.5~1℃ / h, and hold at that temperature for 2~3 hours.

[0007] Preferably, the saturated precursor solution of the lead-tin mixed perovskite is prepared according to the following steps: dissolving formamidinium hydroiodate, lead iodide, stannous iodide, stannous fluoride and additives in an organic solvent, stirring evenly, and preparing a saturated precursor solution of the lead-tin mixed perovskite. The additive is ammonium thiocyanate; The organic solvent is γ-butyrolactone; The total concentration of the saturated precursor solution was 2.2~2.8 mmol / mL.

[0008] Preferably, the molar ratio of formamidinium hydroiodate, lead iodide, stannous iodide, stannous fluoride and additives is 1:0.5:0.5:0.05:0.03~0.05.

[0009] Preferably, the functionalized substrate includes conductive glass and a hole transport layer disposed on the conductive glass; The hole transport layer is made of poly(3,4-ethylenedithiophene)-poly(styrenesulfonic acid).

[0010] Preferably, the surface of the hole transport layer is further modified with a self-assembled monolayer; the self-assembled monolayer is Me-4PACz.

[0011] Preferably, the antisolvent is chlorobenzene; the applied pressure is 1000~1500 kPa.

[0012] Preferably, the temperature for replenishing the growth medium is between 80°C and 85°C.

[0013] The second objective of this invention is to provide a lead-tin mixed perovskite single-crystal thin film.

[0014] The third objective of this invention is to provide an application of lead-tin mixed perovskite single-crystal thin films in near-infrared detection.

[0015] The fourth objective of this invention is to provide a photodetector comprising a functionalized substrate, a light-absorbing layer, an electron transport layer, and an electrode stacked sequentially; a BCP interface modification layer is disposed between the electron transport layer and the electrode. The light-absorbing layer is a lead-tin mixed perovskite single-crystal thin film; The functionalized substrate includes conductive glass and a hole transport layer disposed on the conductive glass. The hole transport layer is a poly(3,4-ethylenedithiophene)-poly(styrene sulfonic acid) layer, or a composite layer of poly(3,4-ethylenedithiophene)-poly(styrene sulfonic acid) and surface-modified self-assembled monomolecules. The electron transport layer is fullerene C60, and the electrode is a copper electrode.

[0016] Compared with existing technologies, this invention provides a method for preparing lead-tin mixed perovskite single-crystal thin films and their near-infrared detection applications, which has the following significant advantages: (1) The secondary crystal growth strategy overcomes the bottleneck in thick film preparation: In response to the technical difficulties of rapid crystallization rate of lead-tin perovskite and the tendency of residual grain boundary pores due to solute depletion in the later stage of high-temperature growth in the traditional one-step confined growth method, this invention proposes a "secondary crystal growth" strategy. By dynamically replenishing the growth solution during the key growth stage, the pores and defects inside the film are effectively eliminated, and a lead-tin mixed perovskite single crystal film with a smooth surface and dense and continuous interior is successfully prepared.

[0017] (2) Multidimensional defect control and interface optimization improve device performance: This invention effectively controls crystallization kinetics and passivates bulk defects by optimizing precursor solution concentration and additive engineering; at the same time, it optimizes energy level matching by using self-assembled monolayer (Me-4PACz) as hole transport layer.

[0018] (3) High-performance self-driven near-infrared detection is achieved: The single-crystal thin film prepared in this invention has extremely low defect state density and excellent carrier transport characteristics. The photodetector constructed based on this thin film not only extends the response spectrum to the near-infrared band (~1000 nm), but also achieves high-sensitivity detection at zero bias (0 V), demonstrating excellent self-driven operation capability, reducing device power consumption, and has broad application prospects in the field of low-power photoelectric sensing. Attached Figure Description

[0019] Figure 1 Optical photographs and scanning electron microscope (SEM) images of lead-tin single crystal thin films with NH4SCN additive introduced in Example 1(b) and without NH4SCN additive introduced in Comparative Example 1(a); Figure 2 The photoelectric response performance of the photodetectors constructed with lead-tin single crystal thin films with NH4SCN additive in Example 1 and without NH4SCN additive in Comparative Example 1 under 940 nm near-infrared illumination is shown. Figure 3 Optical photographs and SEM images of single-crystal thin films prepared using saturated precursor solutions with concentrations of 2.2M, 2.5M, and 2.8M, respectively, for Examples 2, 3, and 4; Figure 4 The X-ray diffraction (XRD) patterns of single-crystal thin films prepared at saturated precursor solution concentrations of 2.2M, 2.5M, and 2.8M are shown for Examples 2, 3, and 4, respectively. Figure 5 Examples 2, 3, and 4 correspond to the dark current density-voltage ratio of single-crystal thin-film photodetectors at saturated precursor solution concentrations of 2.2M, 2.5M, and 2.8M, respectively. J D -V) Characteristic curve; Figure 6 Optical photographs and SEM images of the single-crystal thin films prepared on Me-4PACz self-assembled monolayers in Example 5; Figure 7 This is a schematic diagram of the photodetector based on the Me-4PACz substrate in Example 5; Figure 8The graph shows the photoelectric response performance of the single-crystal thin-film photodetector based on the Me-4PACz substrate in Example 5 under 940 nm near-infrared illumination. Figure 9 Optical images and SEM images of the single-crystal thin films prepared in Comparative Example 2 using a one-step growth method (without replenishment solution); Figure 10 The XRD pattern of the single-crystal thin film prepared by one growth in Comparative Example 2. Detailed Implementation

[0020] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments and accompanying drawings. However, the embodiments described are not intended to limit the present invention.

[0021] The purpose of this invention is to overcome the problems of numerous grain boundary defects, limited carrier transport, and porosity and discontinuities easily generated during large-area film formation by traditional single-crystal growth methods in existing lead-tin mixed perovskite polycrystalline thin films. This invention provides a method for preparing lead-tin mixed perovskite single-crystal thin films and a self-driven near-infrared detector thereof. This method, through the introduction of antisolvent-assisted induced nucleation and a unique secondary crystal growth strategy, combined with additive engineering and interface modification, achieves the controllable preparation of high-quality, dense, porosity-free, and continuous lead-tin mixed perovskite single-crystal thin films, and based on this, constructs a highly sensitive self-driven near-infrared detector.

[0022] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a lead-tin mixed perovskite single-crystal thin film, comprising the following steps: Preparation of a saturated precursor solution of lead-tin mixed perovskite; An antisolvent is added to a saturated precursor solution to obtain a suspension; the antisolvent is chlorobenzene. The suspension was dropped onto a functionalized substrate, and a uniformly distributed lead-tin mixed perovskite seed layer was formed on the surface of the functionalized substrate by spin coating and annealing. After adding growth solution to a lead-tin mixed perovskite seed layer, a confined space is formed on the seed layer by covering it with a cover plate. Pressure is then applied to the cover plate, and crystal growth is performed by programmed temperature increase. During the temperature increase, growth solution is added to the confined space to induce secondary crystal growth. After the growth is completed, the pressure and cover plate are removed, and the crystal is allowed to cool naturally to room temperature, thus obtaining a lead-tin mixed perovskite single crystal thin film on a functionalized substrate. The applied pressure is 1000~1500 kPa; the temperature for replenishing the growth medium is between 80℃ and 85℃. The growth solution is the clear supernatant of a saturated precursor solution of lead-tin mixed perovskite. The programmed temperature rise is as follows: first, rapidly raise the temperature to 50~65℃ at a rate of 25-30℃ / h, then raise the temperature to 85~95℃ at a rate of 0.5~1℃ / h, and hold at that temperature for 2~3 hours.

[0023] This invention employs a programmed heating strategy of "fast at first, slow later" based on key control methods of inverse-temperature crystallization kinetics. The first stage (rapid heating from 25-30℃ / h to 50-65℃): This stage is the "growth window approaching" process. Since lead-tin mixed perovskite exhibits inverse-temperature solubility in γ-butyrolactone (i.e., solubility decreases with increasing temperature), rapid heating allows the precursor solution to quickly cross the metastable region of low supersaturation, rapidly reaching the initial supersaturation threshold for crystal growth, avoiding the risk of uneven solvent evaporation and impurity adsorption caused by prolonged heat dissipation at low temperatures. The second stage (slow heating from 0.5-1℃ / h to 85-95℃): This stage is the "steady-state growth" process. Within this range, the crystal enters a rapid growth phase. The extremely slow heating rate aims to precisely control the supersaturation of the solution, maintaining it at a low and stable level (the growth region in the LaMer model), ensuring that the rate of solute precipitation matches the rate of adsorption and growth on the crystal surface. This effectively suppresses spontaneous secondary nucleation in the solution, avoids the generation of parasitic grains, and forces the solute to preferentially grow epitaxially on the surface of the pre-made seed crystal, thereby obtaining a large-size, grain boundary-free, and uniformly oriented single-crystal thin film.

[0024] The saturated precursor solution of the lead-tin mixed perovskite is prepared according to the following steps: formamidinium hydroiodate, lead iodide, stannous iodide, stannous fluoride and additives are dissolved in an organic solvent, stirred evenly, and a saturated precursor solution of lead-tin mixed perovskite is prepared. The additive is ammonium thiocyanate; The organic solvent is γ-butyrolactone; The total concentration of the saturated precursor solution was 2.2~2.8 mmol / mL.

[0025] The molar ratio of formamidinium hydroiodate, lead iodide, stannous iodide, stannous fluoride, and additives is 1: 0.5: 0.5: 0.05: 0.03~0.05.

[0026] The functionalized substrate includes conductive glass and a hole transport layer disposed on the conductive glass; The hole transport layer is made of poly(3,4-ethylenedithiophene)-poly(styrenesulfonic acid).

[0027] The surface of the hole transport layer is further modified with a self-assembled monolayer; the self-assembled monolayer is Me-4PACz.

[0028] An exemplary method for preparing a lead-tin mixed perovskite single-crystal thin film includes: (1) Preparation of perovskite precursor solution: dissolve formamidin hydroiodide, lead iodide, stannous iodide, stannous fluoride and additives in an organic solvent, stir evenly, and prepare a saturated precursor solution of lead-tin mixed perovskite; the organic solvent is γ-butyrolactone. (2) Preparation of functionalized substrate: ITO conductive glass is cleaned and surface treated according to standard procedures, and then a hole transport layer is prepared on its surface to obtain a functionalized substrate for crystal growth.

[0029] (3) Preparation of seed layer: Add a small amount of antisolvent to the saturated precursor solution obtained in step (1) to break the thermodynamic equilibrium of the solution and actively induce the precipitation of small crystal nuclei in the solution to form a suspension; take the suspension and drop it onto the substrate in step (2), and form a uniformly distributed lead-tin mixed perovskite seed layer on the substrate surface by spin coating and annealing. (4) Constructing a spatial confinement structure: Add growth liquid to the seed layer obtained in step (3) and quickly cover it with another substrate prepared in step (2) as a cover sheet to form a sandwich structure spatial confinement growth system; the growth liquid is the clear supernatant of the saturated precursor solution prepared in step (1), or it can be understood that the growth liquid is the supernatant taken after the saturated perovskite precursor solution has been left to stand.

[0030] (5) Secondary crystal growth: Apply longitudinal pressure to the spatial confinement structure constructed in step (4) and perform programmed heating to start crystal growth; during a specific stage of the heating process, add growth liquid to the confinement space to induce secondary crystal growth; after the growth is completed, remove the longitudinal pressure and the top cover plate, and allow it to cool naturally to room temperature to obtain a lead-tin mixed perovskite single crystal film; the specific stage refers to the temperature point between 80°C and 85°C. (6) Fabrication of photodetector: Electron transport layer, interface modification layer and metal electrode are deposited sequentially on the surface of the single crystal thin film prepared in step (5) to complete the device fabrication.

[0031] The organic solvent in step (1) is γ-butyrolactone (GBL); the additive is ammonium thiocyanate (NH4SCN); the concentration of the precursor solution is optimized, preferably in the range of 2.2 M ~ 2.8 M, and more preferably 2.5 M, to balance the solute supply and crystallization rate.

[0032] The hole transport layer material in step (2) is selected from poly(3,4-ethylenedithiophene)-poly(styrene sulfonic acid) (PEDOT: PSS); preferably, the surface of the hole transport layer is further modified with a self-assembled monolayer (such as Me-4PACz) to improve the interface energy level matching.

[0033] The antisolvent mentioned in step (3) is an organic solvent that can reduce the solubility of perovskite in the main solvent, preferably chlorobenzene; the amount added is intended to precisely control the precipitation density and size of the crystal nuclei.

[0034] The secondary crystal growth mentioned in step (5) refers to the process of providing a solute source by supplementing the growth solution during the stage when the solvent evaporates and the crystals are initially fused but not yet fully dense, thereby promoting the fusion of grain boundaries and filling of pores.

[0035] A second aspect of the present invention provides a lead-tin mixed perovskite single-crystal thin film.

[0036] The third aspect of this invention provides an application of lead-tin mixed perovskite single-crystal thin films in near-infrared detection.

[0037] A fourth aspect of the present invention provides a photodetector, comprising a functionalized substrate, a light-absorbing layer, an electron transport layer, and an electrode stacked sequentially; a BCP interface modification layer is disposed between the electron transport layer and the electrode; The light-absorbing layer is a lead-tin mixed perovskite single-crystal thin film; The functionalized substrate includes conductive glass and a hole transport layer disposed on the conductive glass. The hole transport layer is a poly(3,4-ethylenedithiophene)-poly(styrene sulfonic acid) layer, or a composite layer of poly(3,4-ethylenedithiophene)-poly(styrene sulfonic acid) and surface-modified self-assembled monomolecules. The electron transport layer is fullerene C60, and the electrode is a copper electrode.

[0038] For example, a photodetector includes: (a) a lead-tin mixed perovskite single-crystal thin film as a light-absorbing layer; (b) a hole transport layer located on one side of the single-crystal thin film; (c) an electron transport layer located on the other side of the single-crystal thin film; and (d) an electrode located outside the hole transport layer and the electron transport layer; wherein the hole transport layer is a PEDOT:PSS layer or a PEDOT:PSS / Me-4PACz composite layer; the electron transport material is fullerene C60, and a BCP interface modification layer is disposed between the electron transport layer and the electrode; and the electrode is a copper electrode.

[0039] It should be noted that, unless otherwise specified, the experimental methods used in this invention are all conventional methods; and the reagents and materials used, unless otherwise specified, are all commercially available.

[0040] Example 1 This embodiment uses an "antisolvent-assisted nucleation combined with secondary crystal growth method" to prepare lead-tin mixed perovskite (FAPb). 0.5 Sn 0.5I3) Single-crystal thin films were studied, and the regulatory effect of functional additive NH4SCN on the crystallization kinetics of lead-tin mixed perovskite was investigated.

[0041] The specific preparation steps are as follows: Step (1): Dissolve formamidinium hydroiodide (FAI), lead iodide (PbI2), stannous iodide (SnI2), stannous fluoride (SnF2), and NH4SCN in GBL according to the stoichiometric ratio; stir thoroughly in a nitrogen glove box to prepare a saturated precursor solution with a concentration of 2.5 M; wherein the molar ratio of FAI, PbI2, SnI2, SnF2, and NH4SCN is 1: 0.5: 0.5: 0.05:0.03; 3 mol of NH4SCN is added relative to the total amount of Pb / Sn.

[0042] Step (2): The ITO conductive glass was placed in ethanol, ultrapure water with cleaning agent, ultrapure water, and ethanol in sequence, and ultrasonically cleaned for 20 minutes in each step to thoroughly remove surface contaminants. The cleaned substrate was dried with high-purity nitrogen and placed in a 60°C oven to dry. Before use, it was subjected to ultraviolet ozone (UVO) surface treatment for 20 minutes to enhance the surface hydrophilicity.

[0043] Step (3): Spin-coat a layer of (PEDOT: PSS) solution (5000 rpm, 50s) onto a cleaned ITO substrate, then transfer it to a hot plate and anneal at 150°C for 15 minutes to form a uniform hole transport layer.

[0044] Step (4): Take the saturated precursor solution obtained in step (1) and add 5 vol% chlorobenzene (CB) as an antisolvent to induce the precipitation of micro-crystal nuclei to form a suspension. Take the suspension and drop it onto the substrate in step (3), spin-coating it using a dynamic spin-coating method (2000-4000 rpm, 60 s), and then anneal it at 80℃ for 10 min to form a uniform and dense seed layer on the substrate surface. Step (5): The clear supernatant of the saturated precursor solution in step (1) is dropped onto the seed layer obtained in step (4) as the growth liquid, and then quickly covered with another substrate prepared in step (3) as the top cover to form a sandwich structure spatial confinement growth system.

[0045] Step (6): Apply a longitudinal pressure of 1300 kPa to the spatially confined structure and perform programmed temperature rise. First, heat to 60°C at a relatively fast rate, then heat slowly at a rate of 0.5°C / h. When the temperature reaches about 82°C, i.e., when the solvent partially evaporates and the crystals begin to fuse, add about 15 µL of fresh growth solution to the edge of the confined space. This growth solution is the supernatant of the saturated precursor solution prepared in step 1 to induce secondary crystal growth, promote grain boundary fusion and densification, and then continue to heat to 90°C and hold for 3 hours.

[0046] Step (7): After growth, cool to room temperature and remove the top cover. Transfer the prepared single crystal film to the vacuum evaporation chamber and sequentially deposit 20 nm of fullerene C60 (as an electron transport layer), 6 nm of BCP (2,9-dimethyl-4,7-diphenyl-1,10-o-diazaphenanthroline, as an interface modification layer) and 100 nm of copper (Cu) (as a top electrode).

[0047] Step (8): Characterize the microstructure of the single crystal thin film prepared in step (6), and test the photoelectric performance of the device prepared in step (7) (940 nm near-infrared, 0V bias).

[0048] Comparative Example 1 Same as Example 1, except that NH4SCN was not added.

[0049] See Figure 1 As shown in Example 1, after introducing NH4SCN (b), the optical photograph of the quasi-single-crystal thin film exhibits a more uniform black mirror gloss; the SEM image shows that the grain boundaries of the film with the additive group are significantly reduced, and the surface smoothness is greatly improved. This indicates that SCN - Ions effectively regulate the crystallization rate and promote the directional fusion of grains.

[0050] based on Figure 1 The performance of thin-film photodetectors under 940 nm near-infrared illumination is as follows: Figure 2 As shown. The device provided in Example 1 exhibits higher photocurrent and lower dark current, and the calculated specific detectivity (D*) is significantly better than that of Comparative Example 1 (without NH4SCN). This confirms that NH4SCN not only improves crystal quality but also effectively passivates Sn vacancy defects at grain boundaries, thereby enhancing the device's sensitivity.

[0051] Example 2 This embodiment, based on the preferred conditions of Example 1 with the addition of 3 mol% NH4SCN, further investigates the effect of precursor concentration on film formation quality.

[0052] The preparation method is the same as in Example 1, except that a saturated precursor solution with a concentration of 2.2 M is prepared.

[0053] Example 3 Same as in Example 2, except that a saturated precursor solution with a concentration of 2.5 M was prepared.

[0054] Example 4 Same as in Example 2, except that a saturated precursor solution with a concentration of 2.8 M was prepared.

[0055] The microstructure, crystallinity, and dark current density-voltage (DCD) ratios of single-crystal thin films and optoelectronic devices prepared using saturated precursor solutions of different concentrations (2.2 M, 2.5 M, 2.8 M) were characterized. J D -V) Characteristic curve test.

[0056] See Figure 3 As shown, at a concentration of 2.2 M, insufficient solute supply resulted in incompletely fused pores in the film; at a concentration of 2.8 M, rapid crystallization led to significant surface roughness and buildup. In contrast, the film prepared at a concentration of 2.5 M exhibited the best density and smoothness.

[0057] See Figure 4 As shown in the XRD patterns of the single-crystal thin films provided in Examples 2-4, all films exhibit a (100) preferred orientation, but the 2.5 M film has the highest diffraction peak intensity and the narrowest half-width, indicating that the crystal growth quality is optimal at this concentration.

[0058] See Figure 5 As shown, the dark current density-voltage ratio of devices with different concentrations is illustrated. J D The -V curves correspond to Examples 2(a), 3(b), and 4(c), respectively. Figure 5 It can be seen that the 2.5 M device has the lowest dark current density, indicating that the high-quality non-porous film effectively suppresses leakage current.

[0059] Example 5 This embodiment investigates the effect of substrate Me-4PACz interface modification on crystal growth and device performance.

[0060] The preparation method is the same as in Example 3, except that... In step (3): After preparing the PEDOT:PSS hole transport layer and annealing it, a Me-4PACz self-assembled monolayer is further spin-coated onto its surface as an interface modification layer. Specifically, Me-4PACz ethanol solution (concentration of about 1 mmol / L) is spin-coated onto the PEDOT:PSS hole transport layer on a UVO-treated ITO substrate and annealed at 100℃ for 10 min.

[0061] The microstructure of the single-crystal thin film prepared on the self-assembled monolayer of Me-4PACz was characterized, and the photoelectric performance of the prepared photodetector was tested (940 nm near-infrared, 0V bias).

[0062] See Figure 6As shown, the quasi-single-crystal thin film grown on the Me-4PACz substrate maintains excellent compactness. This is because Me-4PACz improves the substrate surface energy, resulting in a tighter contact between the crystal and the substrate.

[0063] See Figure 7 The diagram shows a schematic of the device structure based on Me-4PACz.

[0064] The device consists of, from bottom to top, an ITO layer, a PEDOT:PSS layer, a SAMs layer (Me-4PACz layer), a Pb-Sn Mixed Perovskite layer, a C60 layer, and a Cu electrode.

[0065] Figure 8 Performance tests show that the device exhibits further improved zero-bias responsivity and excellent self-driving performance under 940 nm near-infrared illumination, with a specific detectivity D* reaching 4.5 × 10⁻⁶. 13 Jones. This is attributed to the better energy level matching between Me-4PACz and lead-tin perovskite, which reduces interfacial energy loss and passivates bottom interfacial defects.

[0066] Comparative Example 2 Preparation of lead-tin hybrid single-crystal thin films using a one-stage growth strategy This comparative example aims to verify the key role of the core strategy of this invention, "secondary crystal growth," in eliminating porosity in thick films.

[0067] The preparation method is different: the same raw material ratio, substrate treatment and antisolvent-assisted seed preparation process as in Example 3 (Group 2.5 M) are used. The only difference is in step (5): during the spatial confinement growth process, the operation of "replenishing growth solution" is not performed, and the initially constructed confinement structure is directly heated from room temperature to 90°C and kept at that temperature.

[0068] The microstructure and crystallinity of single-crystal thin films prepared by a one-step growth method (without replenishment) were characterized. See [link to relevant documentation]. Figure 9 As shown, the thin film prepared by the one-step growth method exhibits a large area of ​​porosity in the central region of the optical image, while the SEM image clearly shows numerous unclosed deep pores and trenches at the grain boundaries. This is because, during the later stages of long-term high-temperature growth, the solute in the confined space is depleted without external replenishment, preventing the grains from completing the final fusion and densification.

[0069] See Figure 10 As shown in the XRD pattern, the diffraction peak intensity of the comparative film is significantly lower than that of the secondary-grown film in Example 3, confirming its poor crystal density and demonstrating the key role of the secondary crystal growth (liquid replenishment) strategy in eliminating porosity in thick films.

[0070] In summary, this invention provides a method for preparing a lead-tin mixed perovskite single-crystal thin film and its self-driven near-infrared detector. Addressing the problems of rapid crystallization rate and high defect density in existing lead-tin perovskite films, this invention proposes a novel preparation process combining antisolvent-assisted nucleation and secondary crystal growth. This method introduces an antisolvent into a saturated precursor solution to prepare a high-quality seed layer, and dynamically replenishes the growth solution during the critical stage of spatially confined growth, effectively solving the grain boundary porosity problem caused by solute depletion, and successfully preparing a dense, non-porous, and continuous lead-tin mixed perovskite single-crystal thin film. Further optimization of the precursor solution concentration, ammonium thiocyanate additive, and Me-4PACz interface modification significantly reduces the defect state density of the film. The photodetector constructed based on this film achieves high-sensitivity self-driven detection under zero bias in the 940 nm near-infrared band, exhibiting low dark current and high specific detectivity, and has broad application prospects in the field of low-power photoelectric sensing.

[0071] Although embodiments of the present invention have been shown and described above, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a lead-tin mixed perovskite single crystal thin film, characterized in that, Includes the following steps: Preparation of a saturated precursor solution of lead-tin mixed perovskite; Adding an antisolvent to a saturated precursor solution yields a suspension; The suspension was dropped onto a functionalized substrate, and a uniformly distributed lead-tin mixed perovskite seed layer was formed on the surface of the functionalized substrate by spin coating and annealing. After adding growth solution to a lead-tin mixed perovskite seed layer, a confined space is formed on the seed layer by covering it with a cover plate. Pressure is then applied to the cover plate, and crystal growth is performed by programmed temperature increase. During the temperature increase, growth solution is added to the confined space to induce secondary crystal growth. After the growth is completed, the pressure and cover plate are removed, and the crystal is allowed to cool naturally to room temperature, thus obtaining a lead-tin mixed perovskite single crystal thin film on a functionalized substrate. The growth solution is the clear supernatant of a saturated precursor solution of lead-tin mixed perovskite. The programmed temperature rise is as follows: first, rapidly raise the temperature to 50~65℃ at a rate of 25-30℃ / h, then raise the temperature to 85~95℃ at a rate of 0.5~1℃ / h, and hold at that temperature for 2~3 hours.

2. The method for preparing lead-tin mixed perovskite single crystal thin films according to claim 1, characterized in that, The saturated precursor solution of the lead-tin mixed perovskite is prepared according to the following steps: formamidinium hydroiodate, lead iodide, stannous iodide, stannous fluoride and additives are dissolved in an organic solvent, stirred evenly, and a saturated precursor solution of lead-tin mixed perovskite is prepared. The additive is ammonium thiocyanate; The organic solvent is γ-butyrolactone; The total concentration of the saturated precursor solution was 2.2~2.8 mmol / mL.

3. The method for preparing lead-tin mixed perovskite single crystal thin films according to claim 2, characterized in that, The molar ratio of formamidinium hydroiodate, lead iodide, stannous iodide, stannous fluoride, and additives is 1: 0.5: 0.5: 0.05: 0.03~0.

05.

4. The method for preparing lead-tin mixed perovskite single crystal thin films according to claim 1, characterized in that, The functionalized substrate includes conductive glass and a hole transport layer disposed on the conductive glass; The hole transport layer is made of poly(3,4-ethylenedithiophene)-poly(styrenesulfonic acid).

5. The method for preparing lead-tin mixed perovskite single crystal thin films according to claim 4, characterized in that, The surface of the hole transport layer is further modified with a self-assembled monolayer; the self-assembled monolayer is Me-4PACz.

6. The method for preparing lead-tin mixed perovskite single crystal thin films according to claim 1, characterized in that, The antisolvent is chlorobenzene; The applied pressure is 1000~1500 kPa.

7. The method for preparing lead-tin mixed perovskite single crystal thin films according to claim 1, characterized in that, The temperature for replenishing the growth medium is between 80℃ and 85℃.

8. A lead-tin mixed perovskite single-crystal thin film prepared by the method according to any one of claims 1 to 7.

9. The application of the lead-tin mixed perovskite single crystal thin film according to claim 8 in near-infrared detection.

10. A photodetector, characterized in that, It includes a functionalized substrate, a light absorption layer, an electron transport layer, and an electrode stacked sequentially; a BCP interface modification layer is disposed between the electron transport layer and the electrode. The light-absorbing layer is the lead-tin mixed perovskite single-crystal thin film as described in claim 8; The functionalized substrate includes conductive glass and a hole transport layer disposed on the conductive glass. The hole transport layer is a poly(3,4-ethylenedithiophene)-poly(styrene sulfonic acid) layer, or a composite layer of poly(3,4-ethylenedithiophene)-poly(styrene sulfonic acid) and surface-modified self-assembled monomolecules. The electron transport layer is fullerene C60, and the electrode is a copper electrode.

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