π-Conjugated Carbazole Cations Enable Wet-Stable Quasi-2D Perovskite Photovoltaics

Quasi-two-dimensional halide perovskites are commonly used in solar cells, as they are more stable than their three-dimensional analogues. Nevertheless, it is still challenging to meet the stability requirements under high-humidity conditions. Here, we design π-conjugated carbazole (CA) cations to increase the water resistance of perovskite. We control the crystallization kinetics by the anti-solvent strategy to locate the hydrophobic low-⟨n⟩-value phase on the surface of the perovskite film. The resulting CA2MA4Pb5I16 film does not decompose after being immersed in water for several minutes. We further regulate the vertical orientation of perovskite crystals by introducing NH4SCN additive, resulting in improved carrier transport dynamics. As a result, the optimized CA2MA4Pb5I16 device achieves a notable power conversion efficiency (PCE) of 18.23% and retains more than 85% of the original PCE after 2000 h under a relative humidity of 65% at 25 °C. This is one of the most stable reported unencapsulated perovskite solar cells in high-humidity environments.