Synthesis And Optoelectronic Properties Of Novel All-Inorganic Halide Perovskites

Due to the advantages of suitable band structure,unique tolerance to defect states,low cost and easy processing,halide perovskites have widely studied for optoelectronic applications,especially solar cells,in recent years.However,the intrinsic thermal insta-bility of organic-inorganic hybrid halide perovskites severely hinders their development.The investigation of all-inorganic halide perovskites is therefore important with strategic significance.This study starts from the investigation of thermal degradation mechanism in hybrid perovskite solar cells,which emphasizes the key solution to thermal stabil-ity improvement of devices by using all-inorganic halide perovskites.Targeting on the phase stability problem of CsPbI3,the most potential one among the all-inorganic halide perovskites,we then develop a thermodynamically controlled material growing method induced by the vacancy defects of inorganic matrix.Finally,we rationally explore and syn-thesize a novel 2D halide perovskite,Cs2PbI2Cl2,with the guiding thought of dimensional control,and study its optoelectronic properties systematically.The main research contents and innovations are as follows:(1)Based on the inverted structure perovskite solar cells,this study focuses on the high temperature diffusion behavior of I-and MA+ions from the perovskite layer and their interfacial reactions with the electrode.An electrode-induced thermal degradation mechanism is proposed here,based on the results of morphology,conductivity and car-rier transfer ability change of the perovskite thin films.Moreover,with the established connection between the thermal decomposition of materials and the thermal degradation of devices,we are able to provide the fundamental rules towards thermally stable devices.(2)The first observation of the spontaneous formation of nanoscale ?-CsPbI3(perovskite phase)at room temperature is reported using Cs4PbI6 matrix.A?-CsPbI3@Cs4PbI6 structure model is given,followed by a thorough study of its structural and optical properties.We find that this structure is able to grow in all Cs4PbX6(X=Cl,Br,I)matrixes and combining structural analysis,we provide a defect-inducing growth mechanism,which explains the thermodynamic spontaneity and vacancy-assisted control of forming ?-CsPbI3.The rigid Cs4PbI6 matrix,in the meantime,protect the inside?-CsPbI3 structures from phase transition by thermodynamically increase the transition energy barrier,endowing them with good tolerance towards humidity,illumination and high temperature.(3)The first 2D all-inorganic halide perovskite,Cs2PbI2Cl2,is synthesized as we rationally explore the model system of Cs2PbX4(X=Cl,Br,I).A systematical study of optoelectronic property is performed with Cs2PbI2Cl2 single crystals,as well as the UV light and ? particle response experiments,which expands the radiation detection application of halide perovskites.Combining theoretical calculations and experimental results,we investigate the structural stability of 2D halide perovskites from the aspects of X-site halogen occupation,B-site replacement by Sn2+and A-site cation size,and we evaluate the thermal and environmental stability of materials at last.