Research On The Gas-phase Compositional Modulation And Photovoltaic Property Of Cs-based Perovskite Solar Cells

In recent years,the organic-inorganic hybrid CH₃NH₃PbI₃?MAPbI₃?perovskite materials have attracted the attention of many researchers in the photovoltaic field because of their suitable optical band gap,excellent carriers transport ability and high absorbance,but its poor humidity and thermal stability is difficult to overcome simultaneously.The results show that the replacement of MA⁺in MAPbI₃ with FA⁺or Cs⁺can effectively improve the thermal stability of perovskite materials.The Br^-substitution of I^-can improve the humidity stability.The doping of Cl can effectively improve crystal quality and carriers transport length of the perovskite films.However,the conventional solution method encounters problems such as difficulty in precisely controlling the composition of the film,difficulty in controlling the liquid phase reaction,and low solubility of the Br compound.In order to solve the above problems,this dissertation used a chemical vapor deposition method to prepare a mixed cation Cs_xFA_1-xPbI₃ perovskite thin film and a solar cell based on the same.At the same time,an innovative vapor-assisted gas-assisted Br₂ injection process was developed to prepare inorganic CsPbBr₃ thin films and devices.In addition,the growth mechanism of Cl^-doped perovskite films was explored.The content of this thesis mainly includes:First,Fabrication of Cs_xFA_1-xPbI₃ mixed-cation perovskites via gas-phase-assisted compositional modulation for efficient and stable photovoltaic devices.The precursor films of Cs_xPbI_2+x were first spin-coated by solution method,and then the FAI was heated to volatilize into the vapor phase and gas-solid phase reacted between the FAI and the Cs_xPbI_2+x precursor film,The results show that the content of Cs⁺in the film is the key to the formation of pure phase Cs_xFA_1-xPbI₃.Pure phase Cs_xFA_1-xPbI₃ can be obtained in the range of 0<x<0.30.When x>0.3,the phase separation occurs and CsPbI₃ phase.At the same time,the cell volume of Cs_0.15FA_0.85PbI₃ is the smallest when the content of Cs⁺is0.15,and the stability of the cell is the best.Based on the calculated results,the PCE of solar cell is 14.45%.After a week of testing,More than 90%of the level.Second,Investigation of the effect of chlorine doping on the vapor-assisted growth mechanism of films and its performance of MA_0.85Cs_0.15PbI_3-xCl_x solar cells.Cl element was introduced into the precursor thin film Cs_0.15PbI_2.15-xCl_x by using inorganic compound CsCl as Cl source,and then MAI was introduced into the perovskite thin film by chemical vapor deposition?CVD?.The Cs_0.15PbI_2.15-xCl_x precursor film and MA_0.85Cs_0.15PbI_3-xCl_x thin films were characterized and compared by XRD,SEM,SRPES and other methods.It was found that the Cl elements should exist in the precursor film,when the perovskite films formed after the CVD treatment,Cl elements will disappear.Similarly,the Cl element only affects the crystal structure and the surface morphology of the precursor film,and only plays a role in assisting the crystallization of the MA_0.85Cs_0.15PbI_3-xCl_x perovskite film.Third,Fast anion-exchange from CsPbI₃ to CsPbBr₃ via Br₂-vapor-assisted deposition for air-stable all-inorganic perovskite solar cells.We develop a facile Br₂ vapor hot-injection method to realize fast gas-phase anion-exchange from CsPbI₃ to CsPbBr₃.On this basis,all-inorganic perovskite solar cells prepared by FTO/c-TiO₂/m-TiO₂/CsPbBr₃/Carbon structure achieved 5.38%power conversion efficiency.After 21days of stability test,the devices efficiency were maintained about 90%of the level.