Study On The Growth Of CsPbI_3-xBr_x Perovskite Films By Crystal Engineering

All-inorganic perovskite materials have been rapidly recognized in the field of optoelectronics due to their excellent high temperature stability and chemical stability.Especially,the mixed-halide perovskite materials of I and Br(such as CsPbI3-xBrx)can optimally adjust the band gap by adjusting the halogen composition,providing a suitable material system for perovskite/silicon tandem solar cells.However,the CsPbI3-xBrx perovskite polycrystalline thin films prepared by traditional methods have some shortcomings,such as poor crystal quality,high grain boundary concentration,high surface defect density and uneven grain orientation.And they are prone to severe halide phase segregation under illumination,which brings a serious impact on the photoelectric performance and durability of the films and devices.Therefore,exploring the growth of high-quality CsPbI3-xBrx films with good crystallinity,high-flatness surface,low-density grain boundaries and defects,well-fused grain boundaries,and uniform orientation is crucial for perovskite-based optoelectronic devices.Herein,by the pressure-enhanced particle diffusion,taking the hot-pressing crystal growth method in confined space as the starting point and based on the preparation of high-quality CsPbI3-xBrx thin films,we studied the mechanism of inhibiting photoinduced phase segregation,proposed a thin film growth strategy for inhibiting photoinduced phase segregation of mixed-halide perovskite,and developed a high-performance CsPbI3-xBrx film-based self-driven photodetector.The main research contents and conclusions of this thesis are as follows:1.By deeply analyzing the causes of photoinduced phase segregation of mixed-halide perovskite materials,we designed a thermal-pressing(TP)crystal growth strategy,and grown a series of high-quality CsPbI3-xBrx films with single-crystal-like surface.These films have the characteristics of large grain size(tens of microns),high film crystallinity,uniform orientation,deep fusion of grain boundaries,single-crystal-like surfaces,and low-density traps.The fully merged growth of grains and the well-fused of grain boundaries effectively eliminate the channels of photoinduced halide ion migration.The photoinduced phase segregation process was analyzed by fluorescence spectrum,and the correlation between the structural characteristics,physical properties of the films and the inhibition of phase segregation was explored.It was found that the CsPbI3-xBrx films grown by thermal-pressing(TP)did not exhibit obvious photoinduced halide phase segregation under continuous laser irradiation,and the films had ultra-high environmental stability.This work provides a material guarantee for suppressing the photoinduced halide phase segregation of mixed-halide perovskite materials and constructing efficient and stable perovskite-based optoelectronic devices.2.Based on the above-designed thermal-pressing(TP)crystal growth method,we prepared a uniaxially oriented CsPbIBr2 film composed of large-sized grains(2-3μm)on the surface of ITO/SnO2,investigated the effects of TP growth parameters on the structure and physical properties of the films performance and optimized growth parameters.The film has the characteristics of high crystallinity,single-crystal-like surface morphology,deep fusion of grain boundaries,low-density defects,and long carrier lifetime.Combined with the device structure design,the self-driven photodetector developed based on this film exhibited good optoelectronic properties,including a ultra-high on-off ratio(7.7×106),high responsivity(0.86 A/W)and detection rate(2.65×1013 Jones),which is superior to the performance of most reported perovskite film self-driven devices.At the same time,the removal of a large number of grain boundaries and the deep fusion of grain boundaries effectively inhibit the photoinduced phase segregation of halides in the mixed-halide film.Combined with the good hydrophobic properties of the film,the thin film device had great light and humidity stability.The perovskite film-based self-powered detector with high responsivity,fast response speed,low detection limit and good stability is expected to have potential application value.Moreover,the high-quality films grown by the TP method will surely provide a reference for the development of high-performance photovoltaic devices.