Controllable Growth And Optoelectronic Properties Of Halide Perovskite Single Crystal Wafers

In recent years,halide perovskite materials have been widely used in the research of highperformance solar cells and detectors due to their high absorption coefficient,long carrier diffusion length,and high carrier mobility.At present,perovskite optoelectronic devices are generally based on polycrystalline thin films,whose grain boundaries are rich in charge defects;and the grain boundaries are channels for water and oxygen diffusion and ion migration,which adversely affects the performance of the device.For example,polycrystalline perovskite cells often have hysteresis in the current-voltage（J-V）curve and poor stability.Compared with polycrystalline films,perovskite single crystals have better optoelectronic properties and higher stability due to the elimination of grain boundaries.Therefore,perovskite single crystals are ideal materials for the preparation of high-performance optoelectronic devices.After just 5 years of development,the efficiency of single-crystal perovskite solar cells（PSCs）has rapidly increased from 6.5%to 22.8%.In addition,single-crystal perovskite X-ray detectors have the advantages of high sensitivity and low detection limit,and the performance is significantly better than that of commercial amorphous selenium detectors.However,there are still some problems in the development of perovskite single crystal cells and detectors,such as:（1）The efficiency and stability of single crystal perovskite solar cells are not high,especially the stability is very poor,which contradicts the excellent stability of perovskite single crystal materials,and the internal mechanism is still unclear.（2）The current perovskite X-ray detectors with excellent performance are generally based on large-sized bulk single crystals,whose large thickness not only reduces the vertical carrier collection,but also causes severe lateral crosstalk.In addition,the integration of bulk single crystals with transistor array substrates is difficult,which limits its imaging applications.In view of the above problems,this thesis adopts the strategy of spatial confinement and liquid level control,combined with the temperature inversion crystallization method to grow perovskite single crystal wafers with controllable thickness,and the optical and electrical properties of the single crystal wafers are studied in detail.Based on the grown single crystal wafers,high-efficiency and stable single-crystal cells and high-sensitivity X-ray detection devices are fabricated.The main research contents are as follows:（1）First,20-μm MAPbI₃ and FA_0.55MA_0.45PbI₃ single crystal wafers were grown by combining space-confined method and inversion crystallization strategies.Through studies of cell stability,crystal quality,and charge defect density,we reveal the underlying reasons for the poor stability of widely studied 20-μm monocrystalline cells.The higher defect density of single crystal wafers provides a large number of channels for ion migration,which further degrades the material properties.（2）Subsequently,the quality of FA_0.55MA_0.45PbI₃ single crystal wafers is improved,the defect density of wafers is reduced,the activation energy of ion migration is improved,and the degradation of photoinduced material properties is weakened by adjusting the diffusion rate of solute in the confined space.The efficiency of single crystal cell based on high quality single crystal cell does not decrease obviously after running continuously for 330 h at maximum power point under one solar illumination.At the same time,it is also found that the carrier transport length of FA_0.55MA_0.45PbI₃ single crystal solar cells is more than 200 μm,which is conducive to the development of lateral-structure PSCs.（3）By controlling the distance between the solution surface and the ITO substrate,a MAPbBr₃ single crystal wafer with a thickness of millimeters and an inch size is directly grown on an indium tin oxide（ITO）substrate.Then,by polishing and ozone（O3）treatment,single crystal wafers with smooth surface,low defect state density and good electrical properties were obtained.The prepared X-ray detector is highly sensitive,with a sensitivity of 632 μC Gy_air^-1 cm^-2 under a bias of-5 V.This work provides an effective way to prepare perovskite single crystal X-ray detectors that can be integrated with the substrate,large area,and thickness controllable,which is beneficial to the development of practical applications of perovskite single crystal imaging.