Suppressing the penetration of 2D perovskites for enhanced stability of perovskite solar cells

In recent years, perovskite solar cells (PSCs) have shown rapid development, bringing them closer to commercialization. Surface passivation has proven critical in enhancing device performance due to the higher defect density at the film surface compared to the bulk. Introducing 2D perovskite layers is a widely adopted passivation strategy; however, the penetration of large organic cations into the underlying 3D perovskite layer can hinder charge transport and damage the film structure. In this work, we modified the commonly used ammonium salt PEAI by introducing fluorine atoms at various positions on the benzene ring (o-FPEAI, m-FPEAI, and p-FPEAI) and investigated their effects on passivation and stability. Our results show that m-FPEAI effectively inhibits the penetration of the 2D phase, improving charge transport and device stability due to a strong steric effect. Photoluminescence (PL) and transient absorption (TA) spectroscopy confirmed that m-FPEAI-treated films exhibited superior suppression of non-radiative recombination and enhanced stability under ambient conditions. Devices incorporating m-FPEAI achieved a maximum power conversion efficiency (PCE) of 24.63% and retained over 80% of their initial efficiency after 1750 hours of continuous illumination. This study demonstrates the critical role of fluorine positioning in optimizing surface passivation and offers valuable insights for further improving PSC performance and stability.