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

Abstract 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) 2 FA 3 Pb 4 I 13 PSCs achieve a power conversion efficiency (PCE) of 19.24%, while BZA‐based PSCs ((BZA) 2 FA 3 Pb 4 I 13 ) 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 °C thermal stability of (DF‐BZA) 2 FA 3 Pb 4 I 13 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.