Vapor Deposition Of Cesium Lead Bromine Perovskite Films And Their Optoelectronic Devices

As a new candidate of semiconductor material,organic-inorganic hybrid perovskite has become a hotspot since it was first introduced into perovskite solar cells owing to its high light absorption coefficient,high carrier mobility,small exciton binding energy and adjustable band gap.Organic-inorganic perovskite solar cells have achieved high power conversion efficiency(PCE),but are inferior in stability to inorganic perovskite.Therefore,to improve the stability and PCE of inorganic perovskite solar cells simultaneously,the preparation process,defect passivation and energy level regulation are studied.At the same time,the perovskite materials are the ideal candidates to construct high performance photodetectors due to the low defect density,high carrier mobility and high light absorption coefficient of the perovskites.In this dissertation,uniform cesium lead bromine inorganic perovskite films prepared by vapor deposition were applied to solar cells and photodetectors.The main results are listed as follows:1.Cesium Lead Bromine inorganic perovskite films were prepared by step vapor deposition.By precisely controlling the thickness of Cs Br and PbBr₂,the uniform Cs Br thin film was first coated on the substrates and covered with PbBr₂ thin film using the thermal evaporation coating equipment.The CsPbBr₃ film was obtained with a Cs Br:PbBr₂ ratio of 1:1.Increasing the thickness of PbBr₂,excessive PbBr₂ could react with the synthesized CsPbBr₃ to form the derivatized phase Cs Pb₂Br₅ at the grain boundary of the CsPbBr₃ film.The results showed that another derivatized phase was formed when Cs Br was excessive,and a CsPbBr₃-Cs₄PbBr₆ complex film was obtained when vapor-depositing 50 nm Cs Br and 40 nm PbBr₂.2.The prepared CsPbBr₃-Cs Pb₂Br₅ inorganic perovskite films were used as light absorbing layers of perovskite solar cells.Cs Pb₂Br₅ at the grain boundary of the surface of CsPbBr₃ films could effectively passivate the grain defects,reduce the implantation energy barrier of the electron transport layer,and inhibit the recombination of the interface between the perovskite layer and the hole transport layer.CsPbBr₃ films containing derivative phase Cs Pb₂Br₅ were obtained with a Cs Br:PbBr₂ ratio of 1:1.1,which resulted in a perovskite solar cell power conversion efficiency up to 8.34%with an open circuit voltage of 1.296 V.The vapor deposition method could avoid the influence of the organic solvent on the film formation of the perovskite,and the stability of the inorganic perovskite material make the battery still perform well after being placed in the air for 1000 h.3.A novel self-driven deep ultraviolet photodetector was constructed with CsPbBr₃-Cs₄PbBr₆ perovskite film as the down-conversion window layer and MAPb I₃ hybrid perovskite as the light-harvesting layer.The working mechanism has been analyzed as follows.Usually,the photodetectors of perovskite materials perform excellently in the ultraviolet to visible spectrum,but have poor detection capabilities in the deep ultraviolet region(200-300 nm),however,Cs₄PbBr₆ demonstrate high absorption in the deep ultraviolet region.The CsPbBr₃-Cs4PbBr₆ film prepared on the back surface of FTO absorbs deep ultraviolet light effectively and converts high energy photons into one or more low energy photons.Low energy photons can pass through the FTO layer to be captured by the hybrid perovskite film,while the presence of Cs₄PbBr₆ greatly enhances the down conversion process.This innovative structure results in a high responsivity of49.4 m A/cm² at 254 nm ultraviolet and a fast response time of 7.8/33.6?s,and no additional power supply is required.Providing a new way to mass produce high-performance deep ultraviolet photodetectors.