Enhancing performance and stability of perovskite solar cells through interface dipole engineering with perfluorinated ammonium salts

Despite significant progress in perovskite solar cells (PSCs), non-radiative recombination losses caused by deep energy level defects in perovskite films and energy barrier between the perovskite layer and the hole transport layer remain the primary obstacles limiting further enhancement of their power conversion efficiency and longterm stability. In this study, by employing density functional theory calculations, we investigated the impact of the number of fluorine groups on the electron cloud distribution and dipole moment within passivated molecules, specifically methylammonium with varying perfluoroalkyl chain lengths (CH2NH3(CF2)nCF3, n = 2,5 and 7). The results demonstrate that 1,1-H-perfluorodecyl iodide ammonium (PFDAI) exhibits the optimal dipole moment and serves as a passivating agent for the perovskite film, possessing exceptional defect passivation capability and significant hydrophobicity. The synergistic effect of perfluorocarbons and ammonium groups on FA+ and uncoordinated Pb2+ serves to adjust the Fermi level of the perovskite film and the energy barrier for hole transition, thereby promoting charge carrier migration. As a result of these enhancements, the efficiency of the solar cells ultimately increases significantly to 25.15 %. Under conditions of 20 % relative humidity and a temperature of 25 degrees C, the retention rate of the PCE remains as high as 90 % after 1000 h of aging tests.