A method for preparing perovskite wafers based on physical hot pressing and its application

Abstract

This invention discloses a method for preparing perovskite wafers using physical hot pressing and its application. This method utilizes physical hot pressing as an aid and conductive polymer modification. Specifically, during the mechanical pressing process of preparing FAPbI3 wafers, an external heating field and conductive polymer modification are simultaneously introduced. The thermal field, at an appropriate temperature, enhances the crystallinity of the wafers, ultimately yielding highly crystalline and dense perovskite wafers. The resulting wafers can be used in highly sensitive near-infrared (NIR) photodetectors, exhibiting excellent photoelectric performance in the NIR wavelength range.

Description

Technical Field

[0001] The present invention relates to the field of perovskite materials, and in particular to a method for preparing high-efficiency perovskite wafers and their application in photodetectors through physical hot pressing assistance and conductive polymer modification. Background Art

[0002] Near-infrared (NIR) photodetection technology plays a vital role in a variety of fields, including medicine, bioimaging, and environmental monitoring. Conventional and commercial NIR photodetectors are typically made of inorganic narrow-bandgap materials, such as silicon (Si), germanium (Ge), indium gallium arsenide (InGaAs), lead selenide (PbSe), polymers, and graphene. In recent years, organic-inorganic hybrid perovskites have emerged as promising NIR photodetectors due to their unique narrow bandgap, high absorption coefficient, long diffusion length, and low exciton binding energy. The performance of perovskite-based NIR photodetectors depends crucially on their composition and microstructural characteristics, including lattice distortion, crystal orientation, grain size, and morphology. Perovskite polycrystalline thin films are primarily prepared using solution-based methods, which present two major challenges: first, residual phase impurities in the solvent, poor product consistency, high solvent cost, and ecological concerns caused by toxicity; second, nonequilibrium crystallization in perovskite polycrystalline films can lead to defects and lattice stress, ion migration problems caused by uncontrolled crystal orientation, and grain size inhomogeneity. Currently, perovskite single crystals and quasi-single crystals grown using techniques such as spatial confinement and temperature ramping have achieved great success in photodetector and photovoltaic applications. However, these methods suffer from low yields, lengthy crystal growth processes, and precise requirements for external temperature conditions, significantly limiting their widespread application in photodetectors and solar cells.

[0003] FAPbI3 (formamidinium lead iodide) is an important perovskite material with a low bandgap of approximately 1.45 eV, making it ideal as a light-absorbing material. Its spectral response extends to the near-infrared region (850 nm), encompassing the energy range of sunlight, thereby optimizing photoelectric conversion efficiency. Under laboratory conditions, the highest cell efficiency has exceeded 27%. It maintains excellent thermal stability at high temperatures, reducing the risk of degradation in practical applications. Its excellent light absorption capacity enables efficient solar energy utilization. Furthermore, FAPbI3 has high electron mobility, which helps increase current output and reduce energy losses. In the field of detectors, FAPbI3 exhibits high sensitivity and a wide wavelength response, making it particularly suitable for imaging and photodetector applications under low-light conditions. Its superior performance makes it a popular choice for next-generation optoelectronic materials. Previous studies have demonstrated that solution-processed FAPbI3 thin-film photovoltaic devices exhibit high signal output and low noise current. However, research on perovskite photodetectors based on FAPbI3 remains limited, primarily due to the α→δ phase transition that occurs in FAPbI3, which affects device performance. In addition, the presence of a large number of grain boundaries and high surface defect state density in perovskites can lead to severe non-radiative recombination and ion migration, limiting the practical application of perovskite optoelectronic devices. Therefore, the research focus of preparing FAPbI3 wafers is to suppress phase transitions and minimize defects.

[0004] The production of perovskite wafers is crucial for advancing the development of high-efficiency photovoltaic cells and photodetectors. Perovskite materials have attracted significant attention due to their excellent optoelectronic properties, tunable band gap, and low-cost potential. Currently, common preparation methods include solution processing, vapor deposition, melt processing, self-assembly, and mechanical pressing.

[0005] The solution method is widely used because of its low cost and suitability for large-scale production, but its crystal quality and stability may be problematic. The vapor deposition method can obtain high-quality thin films suitable for high-performance devices, but the equipment is complex and the cost is high. The melting method is suitable for producing high-quality single crystal materials, but the process is complex and energy consumption is high. The self-assembly method has innovative potential in material design, although the technology is not yet mature and industrialization is difficult. The mechanical pressing method applies pressure to the powder material to force it to form a dense crystal structure under high pressure. The advantage of this method is that it can quickly prepare large-sized crystals, while performing well in controlling the density and uniformity of the material. Compared with the solution method, the mechanical pressing method can avoid the influence of the liquid relative to the environment, thereby improving the stability of the material. However, this method may require high energy consumption and complex post-processing processes to ensure the purity and performance of the crystals.

[0006] Patent number CN202310743832.1, "A Method for Preparing Large-Sized Wafer-Level Perovskite Semiconductor Single Crystal Thin Films," describes a novel carbon dot-tin oxide interface layer technology for anchoring perovskite single crystal thin films to achieve large-area epitaxial growth. This method successfully produced high-quality single crystal films with few defects and large areas. However, the patent does not address how to address the phase stability issues of perovskite wafers. Summary of the Invention

[0007] This invention addresses the problems of poor perovskite crystal phase stability and high defect density in traditional processes by providing a method for preparing perovskite wafers and improving their detection performance using physical hot pressing. This method utilizes physical hot pressing assistance and conductive polymer modification. Specifically, during the mechanical pressing process of FAPbI3 wafers, an external heating field and conductive polymer modification are simultaneously introduced. The thermal field at an appropriate temperature enhances the crystallinity of the wafer, ultimately yielding highly crystalline and dense perovskite wafers. High crystallinity resists phase transitions and promotes crystal phase stability. Furthermore, chemical bonding of the conductive polymer passivates defects at the perovskite grain boundaries and enhances charge transport performance. The combined effects of physical hot pressing assistance and conductive polymer modification result in high-quality, large-sized perovskite wafers. The resulting wafers can be used in highly sensitive near-infrared (NIR) photodetectors, exhibiting excellent photoelectric performance in the NIR wavelength range.

[0008] The technical solution of the present invention is:

[0009] A method for preparing a perovskite wafer based on physical hot pressing, the method comprising the following steps:

[0010] Step 1: Preparation of perovskite microcrystalline powder:

[0011] Formamidine iodide (FAI) and lead iodide (PbI2) were dissolved in 2-methoxyethanol (2-ME) and stirred for 11-13 hours until completely dissolved. The mixture was then filtered and the filtrate was heated to 120-150°C and stirred for 2-3 hours. Microcrystals were obtained after the reaction and filtered again. The microcrystals were washed and dried. Finally, the prepared perovskite microcrystals were thoroughly ground into powder.

[0012] Among them, 10 ~ 20 mmol formamidine iodide was added to every 15 mL of 2-methoxyethanol (2-ME), and the molar ratio of formamidine iodide (FAI) and lead iodide (PbI2) was 1:1;

[0013] Step 2: Hot Pressing

[0014] The conductive polymer and perovskite microcrystalline powder were ground for 5-10 minutes, and then pressed at a temperature of 120-130 °C and a pressure of 18-22 MPa for 8-12 minutes to obtain FAPbI3 perovskite wafers;

[0015] The mass ratio of the polymer to the microcrystalline powder is 0.0005-0.0015;

[0016] The perovskite wafer has a thickness of 0.9-1.1 mm;

[0017] The conductive polymer is preferably polyaniline or polyethylene.

[0018] The perovskite wafer prepared by the method is used to prepare FAPbI3 wafer photodetectors. This photodetector exhibits excellent performance indicators and can meet the application requirements of near-infrared photodetection in many fields.

[0019] Using a metal-semiconductor-metal planar structure, 80-100nm gold electrodes are deposited on the surface of the perovskite wafer by thermal evaporation to form a photodetector.

[0020] The detector has an electrode spacing of 300~350 μm, an electrode length of 7.4~7.5 mm, and an electrode width of 350~400 μm.

[0021] The essential features of the present invention are:

[0022] This method combines traditional mechanical pressing with a physical thermal field (120°C hot pressing) and chemical bonding (conductive polyaniline), overcoming the limitations of traditional methods in controlling crystallization and defect density. Furthermore, this method enables the preparation of inch-scale perovskite wafers with high crystal quality, high phase stability, high absorption efficiency, and low defect density, laying the foundation for the future large-scale production of large-area perovskite optoelectronic integrated devices.

[0023] The preparation principle of the present invention is as follows:

[0024] Physical hot pressing stabilizes the crystal phase: During the fabrication process, hot pressing at 120°C plays a key role in stabilizing the FAPbI3 crystal phase. The hot pressing process induces physical changes in the perovskite powder under high temperature and pressure, causing the grains to re-fuse and grow, thereby reducing the number of grain boundaries and improving crystallinity. This physical effect helps suppress the α→δ phase transition of FAPbI3, ensuring a stable crystal structure in the wafer and laying the foundation for subsequent high-performance photodetection.

[0025] Polymer chemical bonding passivates defects: During the hot pressing process, chemical bonds form between the conductive polymer and FAPbI3. This interaction not only reduces defect formation but also effectively inhibits ion migration. Simultaneously, the polymer is evenly distributed across the wafer, filling grain boundaries and passivating them, thereby reducing the probability of non-radiative recombination and further enhancing the wafer's overall stability and optoelectronic performance.

[0026] The beneficial effects of the present invention are:

[0027] High Phase Stability: This method successfully overcomes the problems of crystal phase impurities and high-density defects caused by traditional solution-grown perovskite production methods. Through the synergistic effect of physical hot pressing and chemical modification, the FAPbI3 wafers have excellent phase stability. This allows the wafers to maintain a stable crystal structure and optoelectronic properties over long-term use and under varying environmental conditions.

[0028] Excellent Photoelectric Performance: The FAPbI3 wafer photodetector fabricated based on this invention exhibits exceptional performance. The thermally pressed and conductive polymer-modified perovskite wafer photodetector exhibits rapid response time and stable on-off cycling to 810 nm near-infrared light (with a rise time of up to 6 milliseconds and a fall time of up to 9.5 milliseconds). These performance parameters surpass those of conventional solution-processed perovskite thin-film photodetectors of the same composition (typically 72 milliseconds rise time and 93 milliseconds fall time), meeting the application requirements of near-infrared photodetection in a wide range of fields.

[0029] Large-Scale Production Potential: The preparation method is simple and highly reproducible. By optimizing process parameters, large-scale production of FAPbI3 wafers can be achieved, providing a reliable material foundation for the future development of integrated perovskite optoelectronic devices. This will help promote the widespread application of perovskite materials in optoelectronic fields such as medical imaging, biological detection, and environmental monitoring.

[0030] This invention utilizes a strategy of hot pressing (120°C and 20 MPa) and chemical bonding (conductive polymer) to effectively address the challenges of crystal phase impurities and high-density defects associated with traditional solution-grown perovskite production methods, thereby improving the phase stability of FAPbI3 wafers. FAPbI3 wafer photodetectors fabricated using this method exhibit excellent photoelectric performance. Furthermore, this method is simple, reproducible, and capable of large-scale production of FAPbI3 wafers, providing a scalable material foundation for future integrated perovskite optoelectronic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of FAPbI3 perovskite wafer photodetector;

[0032] Figure 2 This is a cross-sectional scanning electron microscope image of the physically hot-pressed and polymer-modified FAPbI3 perovskite wafer obtained in Example 1 at a magnification of 1500 times at a scanning voltage of 3 kV;

[0033] Figure 3This is a cross-sectional scanning electron microscope image of the FAPbI3 perovskite wafer obtained in Comparative Example 1 at a magnification of 1500 times at a scanning voltage of 3 kV;

[0034] Figure 4 The transient response time test of the physically hot-pressed and polymer-modified FAPbI3 perovskite wafer detector obtained in Example 1 to 810 nm near-infrared light under a bias voltage of 1 V is shown;

[0035] Figure 5 The transient response time test of the FAPbI3 perovskite wafer detector obtained in Comparative Example 1 to 810 nm near-infrared light under a bias of 1 V;

[0036] Figure 6 The transient response time of the FAPbI3 perovskite thin film detector obtained in Comparative Example 2 to 810 nm near-infrared light under a bias voltage of 1 V is tested;

[0037] Figure 7 The on-off cycle response test of the physical hot pressing and polymer-modified FAPbI3 perovskite wafer detector obtained in Example 1 to 810 nm near-infrared light under a bias of 1 V;

[0038] Figure 8 This is a switching cycle response test of the FAPbI3 perovskite wafer detector obtained in Comparative Example 1 to 810 nm near-infrared light under a bias voltage of 1 V;

[0039] Figure 9 The switching cycle response test of the FAPbI3 perovskite thin film detector obtained in Comparative Example 2 to 810 nm near-infrared light under a bias voltage of 1 V is shown;

[0040] Figure 10 The transient response time of the physically hot-pressed and polymer-modified FAPbI3 perovskite wafer detector obtained in Example 2 to 810 nm near-infrared light under a bias of 1 V is tested;

[0041] Figure 11 The transient response time test of the physically hot-pressed and polymer-modified FAPbI3 perovskite wafer detector obtained in Example 3 to 810 nm near-infrared light under a bias of 1 V. DETAILED DESCRIPTION

[0042] To simultaneously address the phase stability and defect issues within perovskite wafers and fabricate large-area perovskite films or wafers, this paper proposes a novel strategy: through hot pressing and chemical bonding with a conductive polymer, high-quality, inch-scale, large-scale FAPbI3 wafers for highly sensitive near-infrared light detection are achieved. This process is the first universally applicable large-area wafer fabrication method. The polymer is an intrinsically conductive polymer with tunable conductivity, enabling efficient charge transport within the FAPbI3 wafer photodetector, resulting in high photoresponse speed and sensitivity. Physical hot pressing suppresses phase transitions and stabilizes the FAPbI3 crystal phase, while chemical bonding with the conductive polymer passivates defects at the grain boundaries. Finally, the FAPbI3 wafers fabricated using physical hot pressing and conductive polymer modification achieve stable and fast near-infrared light detection. This approach not only addresses the poor phase stability issue within perovskite wafers but also significantly improves their optoelectronic performance, providing a new solution for efficient near-infrared light detection.

[0043] To make the purpose, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention:

[0044] Example 1:

[0045] Fabrication of FAPbI3 perovskite wafer detectors by physical hot pressing and conductive polymer modification

[0046] Step (1): Preparation of FAPbI3 perovskite microcrystalline powder

[0047] Solution preparation: Accurately weigh 15 mmol of formamidine iodide (FAI) and 15 mmol of lead iodide (PbI2) and place them in 15 mL of 2-methoxyethanol (2-ME). Stir continuously for 12 h at a constant temperature of 50°C using a magnetic stirrer to ensure that the two substances are fully dissolved and evenly mixed to form a uniform solution.

[0048] Reaction and Crystallization: The solution was filtered through filter paper to remove any insoluble impurities, yielding a pure precursor solution. The filtered solution was transferred to an oil bath set at 120°C and allowed to react for 2 hours under magnetic stirring. During the reaction, the substances in the solution gradually reacted, forming a large number of black FAPbI3 perovskite microcrystals.

[0049] Post-processing: After the reaction is complete, the solution is filtered again to separate the resulting microcrystals from the solution. The microcrystals are then washed sequentially with 2-ME and isopropyl alcohol (IPA) to remove residual surface impurities and unreacted substances. Finally, the washed microcrystals are dried in a vacuum oven at 100°C to completely remove moisture and residual solvent. The dried FAPbI3 perovskite microcrystals are ground for 10 minutes to a 400-mesh powder for subsequent processing.

[0050] Step (2): Physical hot pressing and conductive polymer modified pressing molding

[0051] A certain amount of polyaniline (PAI) is thoroughly ground into a fine powder, which is then sieved through a 1000-mesh sieve to obtain a polymer powder with uniform particle size. Accurately weigh 1 mg of the sieved PAI and mix it with 1 g of FAPbI₃ powder. The mixture is then thoroughly ground in a mortar for 10 minutes to evenly distribute the PAI throughout the perovskite powder. The mixed powder is then placed in a mechanical press and hot-pressed again at 120°C and 20 MPa for 10 minutes. During the hot-pressing process, the powder particles deform and densify under the high temperature and pressure, initially forming perovskite wafers with a thickness of 1 mm and a diameter of 2 cm.

[0052] Step (3): Preparation of metal counter electrode

[0053] Place the perovskite wafer into the mask of the thermal evaporator. When the gold particles on the evaporation boat are at 5*10 -4 When the vacuum degree is 1.5 Pa, the evaporation rate is controlled at 0.05 nm / s until a gold electrode with a thickness of 80 nm is deposited, completing the preparation of the perovskite wafer detector. Figure 1 As shown, the electrode gap is 300μm, the electrode length is 7.4 mm, and the electrode width is 300μm. This wafer detector has a metal-semiconductor-metal structure. When light shines on the wafer detector, the perovskite layer absorbs light and generates electron-hole pairs. Due to the close contact between the metal and semiconductor layers and the good conductivity of the metal layer, these electrons and holes are extracted to the positive and negative metal electrodes, respectively, forming an electric current.

[0054] Comparative Example 1:

[0055] Preparation of FAPbI3 perovskite wafer detectors by physical hot pressing

[0056] Step (1): Preparation of FAPbI3 perovskite microcrystalline powder

[0057] Exactly the same as the above-mentioned embodiment 1.

[0058] Step (2): Compression molding

[0059] The FAPbI3 perovskite microcrystalline powder was transferred to a customized mechanical pressing device, where a pressure of 20 MPa and a temperature of 120°C were applied to the powder for 10 minutes to form a perovskite wafer with a thickness of 1 mm and a diameter of 2 cm.

[0060] Step (3): Preparation of metal counter electrode

[0061] Exactly the same as the above-mentioned embodiment 1.

[0062] Comparative Example 2:

[0063] Preparation of FAPbI3 perovskite thin film detectors

[0064] Step (1): Preparation of FAPbI3 perovskite film

[0065] 1.6 mmol of formamidine iodide (FAI) and lead iodide (PbI2) were dissolved in 1 mL of dimethylformamide and dimethyl sulfoxide (8:2) and stirred continuously with a magnetic stirrer at 25°C for 2 hours to form a homogeneous perovskite solution. The perovskite solution was then applied to a glass substrate under nitrogen atmosphere using a single-step spin coating process at 5000 rpm for 30 seconds, followed by a vacuum flash evaporation for 30 seconds. The film was then heated at 100°C for 30 minutes, resulting in a FAPbI3 perovskite thin film.

[0066] Step (2): Preparation of metal counter electrode

[0067] Exactly the same as the above-mentioned embodiment 1.

[0068] Based on experimental data, the following will illustrate the morphology and performance improvement effects of the FAPbI3 perovskite wafer detector after physical hot pressing and conductive polymer modification in the present invention.

[0069] Morphological characterization and analysis

[0070] Figure 2 and Figure 3 The following are the scanning electron microscope images of Example 1 and Comparative Example 1 at a scanning voltage of 3 kV and a magnification of 1500 times. Figure 3 In terms of seeing Figure 2 The grain size of FAPbI3 perovskite wafers subjected to physical hot pressing and conductive polymer modification tends to increase. This indicates that the physical hot pressing and conductive polymer modification cause physical changes in the perovskite powder under high temperature and pressure, leading to grain re-fusion and growth, thereby reducing the number of grain boundaries and improving crystallinity. The wafers after hot pressing and polymer modification exhibit significantly larger grain size, fewer grain boundaries, and a smoother surface, demonstrating the effectiveness of physical hot pressing and chemical modification in improving wafer quality.

[0071] Performance testing and analysis

[0072] Figure 4 、 Figure 5 and Figure 6 The transient response time of Example 1, Comparative Example 1, and Comparative Example 2 to 810 nm near-infrared light at a bias voltage of 1 V was tested. The results show that the FAPbI3 perovskite wafer detector, which has undergone physical hot pressing and polymer modification, effectively improves its response speed to near-infrared light, increasing the response time from 16 milliseconds to 6 milliseconds. Compared to Comparative Examples 1 and 2, the detector prepared based on the present invention improves its response time by 2.6 times and 12 times, respectively.

[0073] Figure 7 、 Figure 8 and Figure 9 The on-off cyclic response to 810 nm near-infrared light at a bias voltage of 1 V was tested for Example 1, Comparative Example 1, and Comparative Example 2, respectively. The results show that the FAPbI3 perovskite wafer detector, after physical hot pressing and polymer modification, exhibits more stable on-off stability under illumination, lower dark current, and more stable baseline drift. Compared to Comparative Examples 1 and 2, the detector prepared based on the present invention produces a higher and more stable output current in response to near-infrared light. This improvement in electrical performance can be attributed to the formation of chemical bonds between the polymer and the perovskite, which passivates defects and suppresses carrier recombination.

[0074] Example 2:

[0075] The other steps are the same as in Example 1, except that pressing for 10 minutes is replaced by pressing for 12 minutes;

[0076] The device performance obtained is similar to that of Example 1, such as Figure 10 As shown;

[0077] Example 3:

[0078] The other steps are the same as in Example 1, except that the hot pressing temperature is replaced by 130°C from 120°C;

[0079] The device performance obtained is similar to that of Example 1, such as Figure 11 shown.

[0080] This invention successfully fabricated large, high-phase-purity perovskite wafers. The synergistic effect of physical hot pressing to stabilize the perovskite crystal phase and chemically modifying the polymer to passivate defects improves the response speed and detection capability of the wafer-based photodetector. This wafer-based photodetector exhibits extremely high photoelectric response and operational stability in the near-infrared band, meeting the requirements for efficient photodetection applications.

[0081] Matters not covered by the present invention are known technologies.

Claims

1. A method for preparing a perovskite wafer based on physical hot pressing, characterized in that the method comprises the following steps: Step 1: Preparation of perovskite microcrystalline powder: Dissolve formamidine iodide (FAI) and lead iodide (PbI2) in 2-methoxyethanol (2-ME) and stir for 11-13 hours until dissolved. Filter the mixture and heat the filtrate to 120-150°C and stir for 2-3 hours. Microcrystals are obtained after the reaction and filtered again. After washing, the microcrystals are dried. Finally, the prepared perovskite microcrystals are ground into powder. in, Add 10-20 mmol of formamidine iodide to every 15 mL of 2-methoxyethanol 2-ME, and the molar ratio of formamidine iodide FAI to lead iodide PbI2 is 1:1; Step 2: Hot Pressing The conductive polymer and perovskite microcrystalline powder were ground for 5-10 minutes, and then pressed at a temperature of 120-130°C and a pressure of 18-22 MPa for 8-12 minutes to obtain FAPbI3 perovskite wafers. The mass ratio of the polymer to the microcrystalline powder is 0.0005-0.0015.

2. The method for preparing a perovskite wafer based on physical hot pressing as described in claim 1, characterized in that the thickness of the perovskite wafer is 0.9~1.1 mm.

3. The method for preparing perovskite wafers based on physical hot pressing as described in claim 1, characterized in that the conductive polymer is polyaniline or polyethylene.

4. Application of the perovskite wafer prepared by the method according to claim 1, characterized in that it is used to prepare FAPbI3 wafer photodetectors.

5. The use according to claim 4, characterized in that Using a metal-semiconductor-metal planar structure, a 80-100 nm gold electrode is deposited on the surface of the perovskite wafer by thermal evaporation to form a photodetector. The detector has an electrode spacing of 300~350 μm, an electrode length of 7.4~7.5 mm, and an electrode width of 350~400 μm.

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