Fluorinated Quasi 2D Perovskite Solar Cells with Improved Stability and Over 19% Efficiency

2D Ruddlesden-Popper perovskites (RPP) with excellent environmental and structural stability are emerging photovoltaic materials. Here, a benzylamine-based spacer, namely 3,5-difluorobenzylamine (DF-BZA), is developed for stable and efficient quasi-2D-RP perovskite solar cells (PSCs). Compared to benzylamine (BZA)-based quasi-2D RPP, the DF-BZA-based perovskite film exhibited superior film quality with significantly enlarged grain size and improved charge carrier lifetime owing to the fluorine atoms in DF-BZA. As a result, the optimized (DF-BZA)2FA3Pb4I13 PSCs achieve a power conversion efficiency (PCE) of 19.24%, while BZA-based PSCs ((BZA)2FA3Pb4I13) only achieve a PCE of 17.04%. This represents the champion PCE using FA as the A-site cation in quasi-2D RPPs with n = 4. Moreover, due to the effective insertion of fluorinated spacers into the inorganic layers, the moisture resistance stability and 85 degrees C thermal stability of (DF-BZA)2FA3Pb4I13 are significantly improved. The improvement of photovoltaic performance and stability highlight the great potential of DF-BZA-based spacer for high-performance quasi-2D RP PSCs. A benzylamine-based spacer, namely 3,5-difluorobenzylamine (DF-BZA), is developed for stable and efficient quasi-2D-RP perovskite solar cells (PSCs). Due to the high electron negativity of F atoms, DF-BZA has a higher dipole (12.48 D) than BZA (8.90 D), which is positive to increase the dielectric constant of DF-BZA-based 2D perovskite, resulting in reduced exciton binding energy. As a result, the optimized (DF-BZA)2FA3Pb4I13 PSCs achieved a power conversion efficiency (PCE) of 19.24%. This represents the champion PCE using FA as the A-site cation in quasi-2D RPPs with n = 4. image