Study On Preparation And Performance Of Stable And Efficient Iron Oxide-Based Perovskite Solar Cells

The highest power conversion efficiency as high as 23.7%has been reached for perovskite solar cells?PSCs?after 10 years of development.However,the stability issue is a big difficult problem in front of perovskite devices.The conventional PSCs based on the structure of titanium dioxide—Spiro-OMeTAD has been widely used,but some stability problems exist in this structure.As electron transport layer,titanium dioxide?TiO₂?has many oxygen vacancies as well as the ability of high ultraviolet electron extraction,which gradually decomposes perovskite materials under ultraviolet irradiation;The dopant?e.g.LiTFSI?used in Spiro-OMeTAD hole transport layer has high hydroscopic property,which tends to bring water vapor into perovskite layer and thereby weaken the stability of PSCs.The decomposition of perovskite usually occurs at the defect sites,which result in the fact that the defects of perovskite films are mostly concentrated at the grain boundaries.The increase in the average grain size can effectively reduce grain boundary defects,and thus improve the efficiencies of PSCs.In order to increase the grain size,it is necessary to optimize the crystallization rate of perovskite layer,which can be achieved by the reversible addition reaction between Lewis base and PbI₂.In this thesis,Thiourea,thioacetamide and DMSO were used to optimize the morphology of perovskite layer and efficiencies of PSCs.It can be concluded from experiments that although thioacetamide can promote grain growth,a large amount of thioacetamide is accumulated in the perovskite layer;thiourea can greatly increase the grain size,while the high requirements for experimental operation is needed,and it is difficult to eliminate the hole and grain gap;As Lewis base,DMSO can improve the photovoltaic performance of PSCs and eventually achieving 14%efficiency can be obtained steadily without increasing the process complexity.The stability problems of PSCs are related closely with material properties.In order to improve the stability,two kinds of transport layer materials?e.g.TiO₂ and Spiro-OMeTAD?were replaced,thereby effectively avoiding the stability problems caused by TiO₂ and Spiro-OMeTAD themselves.As a new type of electronic transporting material,hexagonal alpha-Fe₂O₃ has high resistance to ultraviolet light.LAD is selected as dopants in PTAA hole transporting materials,instead of TBP/LiTFSI.This new type of hole transporting material has significantly decreased moisture absorption ability,leading to high resistance to water vapor.In this work,PTAA?LAD?was first introduced into Fe₂O₃based devices.PSCs combining Fe₂O₃-PTAA?LAD?electron-hole transporting layer have the improved ultraviolet and water vapor stability.The power conversion efficiency of the optimized device can reach 13.01%.Besides,while the power of the original conversion efficiency remained above 90%under ultraviolet irradiation for 8 hours or in65⁷0%humidity environment for 9 hours.