Study On Preparation Of All-inorganic Perovskite Photodetector By Vacuum Evaporation Metho

All inorganic halide perovskite CsPbBr₃ has excellent photoelectric properties such as high optical absorption coefficient,adjustable direct band gap,long carrier lifetime and diffusion length,and simple preparation process,good stability,high atomic number and strong anti-radiation ability.It is an ideal material for a new generation of photodetectors.Compared with traditional solution method,vacuum-based dual-source evaporation method is an effective method to prepare Cs Pb Br₃ perovskite films with good uniformity,high surface flatness and easy to achieve large area compact film formation.In this paper,Cs Pb Br₃ perovskite film and its ultraviolet detector and X-ray detector were prepared by double-source evaporation method.Firstly,CsPbBr₃ films and its ultraviolet detector were prepared by double-source co-evaporation method.The effects of different deposition rates of Pb Br₂ to Cs Br on the physical properties of Cs Pb Br₃ films were studied.The results show that when the rate ratio is 1.2,Cs Pb Br₃ films have the highest cubic phase purity and the best crystallization property,but the grain size of the films is small（～100nm）and the grain boundary is obvious.The quality of the film was improved by in situ heating substrate and post-annealing.The results show that the average grain size of the films increases from 100nm to 1μm and the crystallinity of the films is improved with the substrate temperature increasing from room temperature to 200℃.However,the surface root-mean-square roughness increases from 9.0nm to 55.3nm,and the band gap decreases from 2.351e V to 2.343e V.The device performance of Cs Pb Br₃ films UV photodetectors was improved significantly by heating the substrate.When the substrate temperature is200℃,the device has the best performance.The switch,light responsivity,external quantum efficiency and the detection rate were 4.73′10⁴,3.33 A/W,5.56′10¹³ Jones and 1020%,respectively.On the other hand,although post-annealing treatment can also passivate grain boundaries,the improvement effect on device performance is not as obvious as that of in-situ heating substrate,which indicating that in-situ substrate is the most direct and effective way to improve film quality and device performance in dual-source co-evaporation method.Secondly,the CsPbBr ₃ films（20μm thick）X-ray detector was prepared by continuous evaporation method.The effect of the thickness ratio of Cs Br layer to Pb Br₂ layer on the physical properties of Cs Pb Br ₃ thin films was studied.The results show that when the thickness ratio is 0.85,Cs Pb Br ₃films with pure cubic phase structure can be obtained.However,because the internal stress is too large,the film is easy to crack and break away from the substrate.Releasing the internal stress by in-situ heating substrate can effectively solve the problem of film cracking.The dark current of pure cubic phase structure Cs Pb Br ₃ film X-ray detector is too large(10^-9A),which leads to that it impossible to realize the effective detection of X-ray with different dose rate.By introducing Cs Pb ₂Br₅ phase into Cs Pb Br₃ films to form Cs Pb Br₃-Cs Pb₂Br₅ biphase structure film s,the dark current of the device can be reduced by two orders of magnitude(10^{-1 1}A).The best X-ray detector shows a sensitivity of 2320μC Gy^-1cm^-2,and a lowest detectable dose rate of 67n Gys^-1.At the same time,the photocurrent of the device has a good linear relationship with the filament current,voltage of X-ray tube and device bias.