Preparation Of Efficient And Stable Perovskite Solar Cells Using Small Organic Molecules

Organic-inorganic hybrid perovskite materials have attracted much attention due to their many excellent properties,such as high optical absorption coefficient and carrier mobility,flexible band gap,and solution preparation.As early as 2009,Japanese scientists applied perovskite materials to solar cells.Although the efficiency of the cells prepared at that time was only 3.8%,after the efforts of many scientific researchers,the efficiency of perovskite solar cells has reached 25.7%today.This makes more and more people realize the development potential of perovskite cells.However,in inverted（p-i-n）devices,the hole transport material poly（bis（4-phenyl）（2,4,6-trimethylphenyl）amine）（PTAA）is expensive,and there are differences between different production batches of PTAA,which will lead to different device performance when it is put into large-scale applications.In addition,due to the polycrystalline nature of perovskite thin films,many defects are generated during the preparation process,which reduces the efficiency and stability of the device.To solve these problems,the following research is done in this paper.（1）Small organic molecules（C₈-DPNDF）were introduced into inverted perovskite solar cells as an undoped hole transport material（HTM）.C₈-DPNDF exhibits high hole mobility,energy level matching with perovskite,and no dissolution by perovskite precursor solution.The C₈-DPNDF-based device achieved a conversion efficiency（PCE）of 17.5%,while the control device based on widely used（PTAA）as an HTM achieves a conversion efficiency（PCE）of 17.1%.In addition,the C₈-DPNDF-based device can still maintain more than 90%of the initial efficiency after 1 month in ambient air with a relative humidity of 40%.（2）Design and synthesis of ionic liquid compound 9-bromo-6,7-diphenylpyridine[2,1-a]isoquinoline-5-hexafluorophosphate（DPPIQ⁺PF₆^-）,which was introduced into perovskite as an additive.DPPIQ⁺PF₆^-can passivate both grain boundary defects and surface defects of perovskite.The PF₆^-anions are uniformly distributed in the perovskite films and immobilize the organic amine ions through hydrogen bonds,while the DPPIQ⁺cations mainly accumulate on the top surface of the films and bind to[Pb I₃]^-through anion-πinteractions.The best-performing DPPIQ⁺PF₆^-doped device achieves a conversion efficiency of 23.41%,and maintains an initial efficiency of 90%after 1260 hours of continuous sunlight exposure at the maximum power point.