Tailoring Tin‐Based Perovskite Interfaces Through Cold Reductive Plasma

ABSTRACT Tin‐based perovskite solar cells are among the most promising lead‐free alternatives to conventional lead halide perovskites, yet their efficiency remains limited by defects resulting in self‐p‐doping, poor film quality, and instability caused by the oxidation of Sn(II) to Sn(IV). Here, we demonstrate a novel, solvent‐free, low‐temperature reductive plasma treatment to engineer the surface defects of a tin‐based perovskite. By employing a mixed N 2 /H 2 (95%/5%) plasma, we achieve efficient passivation of surface defects, enhancing the open‐circuit voltage ( V OC ) and fill factor (FF) of the corresponding photovoltaic devices and ultimately improving the overall power conversion efficiency (PCE). Photoluminescence (PL) and transient surface photovoltage (trSPV) analyses reveal a strong reduction in non‐radiative recombination and improved charge carrier extraction at the perovskite/electron transport layer interface. Density functional theory (DFT) confirms that hydrogen incorporation into the perovskite lattice forms a stable I‐H‐I bridging motif, mitigating p‐doping and supporting the experimental observations. This work introduces reductive plasma as a scalable and solvent‐free approach to improve the optoelectronic quality of tin halide perovskites, advancing their potential in sustainable photovoltaic applications.