Preparation Of High-Quality CsPbI_3-xBr_x Films And Investigation On Their Photoelectric Performance

Organic-inorganic hybrid perovskites with excellent photoelectric performance have been rapidly developed in the fields of photodetectors,solar cells,lasers and so on.At the same time,all-inorganic perovskites have attracted great interest because of their outstanding stability and similar photoelectric characteristics compared to organic-inorganic hybrid perovskites.For photoelectric devices,the quality of perovskite thin films has become the key to determining device performance.Therefore,it is of great significance to prepare high-quality thin films with large grain size,high crystallinity,and low defect density.In this paper,the all-inorganic mixed halogen perovskite CsPbI3-xBrx is taken as the research object.By proposing a pressure-assisted ion diffusion method,a high-quality CsPbI3-xBrx quasi-single thin film is prepared,and a near-infrared detector with excellent photoelectric properties is developed.The main research contents of the paper are as follows:1.Preparation of CsPbI3-xBrx thin film by two-step method and study of its phase transitionWe first prepared the CsPbI3-xBrx film via two-step spin coating annealing(CA)method.By testing and analyzing its structure,morphology and optical properties,it was found that the film prepared by the CA method has small grain size and high surface roughness,poor crystallinity,and poor performance of photodetectors based on this thin film.In order to investigate the stability of the perovskite phase in the thin film,we first studied the phase stability of the CsPbI3-xBrx thin film by using an isostatic device under specific pressure and temperature conditions.The results show that the perovskite phase of CsPbI3-xBrx film remains stable when heated under normal pressure,but translated to non-perovskite phase when heated at 120? under high pressure.If the surface was covered with silicon wafers,the phase transition when heated to 120? under high pressure was incomplete,and the non-perovskite phase was completely converted back to the perovskite phase in 180?2.The preparation of high-quality CsPbI3-xBrx film and its photoelectric propertiesIn order to improve quality,we proposed a pressure-assisted ion diffusion(PAID)strategy to obtain high-quality CsPbI3-xBrx quasi-single thin film.From the structural test results,it was found that the CsPbI3-xBrx thin film prepared by the PAID method with large grain size,low defect density,strong orientation and deep fusion of grain boundaries.The photodetector prepared by the film has excellent performance:under the irradiation of 532nm laser,the on/off ratio of the detector is as high as 5.75×105,responsivity and detectivity are 4.67×103 mA/W and 4.7×1013 Jones,respectively.3.The research on nonlinear optical properties of CsPbI3-xBrx films and development of near infrared photodetectorWe have studied nonlinear optical properties of the CsPbI3-xBrx film prepared by PAID method with the advantages of low defect density,high crystallinity and orientation,high surface flatness,and high fusion of grain boundaries.Using the open Z-scan technique,the two-photon absorption coefficient(?)of the film was measured and calculated to be 0.94257 cm GW-1.Due to the great two-photon absorption characteristics of the film,a high-sensitivity photoelectric response to the near-infrared region(eg,1030 nm)is realized.