Deuterated FAPbI3 Perovskite Films with Suppressed Deprotonation for Durable Solar Cells
Hybrid perovskite solar cells (PSCs) have reached a certified power conversion efficiency (PCE) of 27.0%, yet their operational lifetime remains constrained by the intrinsic instability of organic cations, particularly the deprotonation of formamidinium (FA). This study introduces a molecular deuteration strategy to stabilize FAPbI3 by substituting the active hydrogen in the N–H bond with deuterium. The reduced ground-state energy of the N–D bond induces a kinetic isotope effect, lowering the deprotonation rate constant from 5.15 × 10−8 to 2.42 × 10−8 s−1. Solar cells fabricated with deuterated FAPbI3 films achieve a PCE of 25.08% and retain 97% of their initial efficiency (T97) for 1264 h under continuous one-sun illumination at 55 °C. This approach addresses the fundamental deprotonation pathway that limits the longevity of FA-based perovskites, offering a viable route to intrinsically stable photovoltaic devices without relying solely on extrinsic barrier layers or passivators.