The lattice deformation and structural evolution of perovskite films in response to electric fields, temperature, and light limit the operational endurance of solar cells. We mechanically reinforced perovskite thin films by integrating a polymer-coupled monolithic single-layer graphene interface that led to a twofold enhancement in modulus and hardness. The synergistic effect of graphene and poly(methyl methacrylate) restricted photoinduced lattice expansion and decreased the deformation ratio from 0.31 to 0.08%, which minimized the structural damage caused by dynamic lattice evolution. Solar cell devices maintained >97% of their initial power conversion efficiency after maximum power point tracking for >3670 hours under full-spectrum air mass 1.5 global (AM 1.5 G) sunlight at 90°C.

Surface engineering has been shown critical for the success of perovskite solar cells by passivating the surface enriched defects and mobile species. The discovery of surface modulators with superior interaction strength to perovskite is of paramount importance since they can retain reliable passivation under various environments. Here, we report a chelation strategy for surface engineering of CsPbI₂Br perovskite, in which dithiocarbamate molecules can be coordinate to surface Pb sites via strong bidentate chelating bonding. Such chelated CsPbI₂Br perovskite can realize excellent passivation of surface under-coordinated defects, reaching a champion power conversion efficiency of 17.03% and an open-circuit voltage of 1.37 V of CsPbI₂Br solar cells. More importantly, our chelation strategy enabled excellent device stability by maintaining 98% of their initial efficiency for over 1400 h in ambient condition. Our findings provide scientific insights on the surface engineering of perovskite that can facilitate the further development and application of perovskite optoelectronics.