Efficient and stable perovskite solar cells via surface passivation of an ultrathin hydrophobic organic molecular layer

•A hydrophobic organic agent is used as a dual-function passivator for perovskites.•The treated device improves the PCE from 19.25% to 20.56%.•The treated device maintains 84% of the initial PCE after 1300 h under 65–75% RH. Organic and inorganic metal halide perovskite solar cells (PSCs) with an outstanding performance of low-cost manufacturing and low-temperature solution processing, have been regarded as the next-generation photovoltaic technology. However, the solution processed perovskite films usually have abundant defects, especially at the grain boundaries and surfaces, causing carrier recombination, hysteresis, and degradation. Herein, 4-(trifluoromethyl)benzylamine (TFMBA) is deposited on the surface of perovskites to form an ultrathin hydrophobic organic molecular layer, passivating the interfacial imperfections. By optimizing the post-treatment conditions, a remarkable power conversion efficiency (PCE) of 20.56% is realized based on Cs0.05(FA0.85MA0.15)0.95Pb(I0.85Br0.15)3 perovskite. Impressively, the passivated ultrathin organic molecular layer effectively prohibits the penetration of moisture, resulting in unsealed PSCs retaining 84% of the original PCE after aged 1300 h at 65%−75% relative humidity (RH). SEM and XRD confirm that TFMBA can effectively passivate defects on the surface and grain boundaries, thereby prevent the perovskites from the irreversible decomposition with the immersion of moisture. This suggests that the TFMBA post-treatment has great potential in obtaining high-quality and stable perovskite films.