Enhanced Stability of All-Inorganic Tin–Lead Perovskite Solar Cells via Additive Engineering

All-inorganic tin–lead halide perovskites (CsPbxSn1–xI3) are promising absorber materials for next-generation photovoltaics due to their near-ideal bandgaps (∼1.3–1.4 eV) and favorable optoelectronic characteristics. Their practical application, however, is limited by intrinsic instabilities, including Sn2+ oxidation, halide migration, and phase transitions. Here, we introduce an additive engineering approach using dimethylammonium iodide (DMAI) to address these challenges. DMAI simultaneously passivates deep-level defects, inhibits Sn2+ oxidation, reduces iodide migration, and improves moisture resistance, thereby enhancing environmental stability. CsPbxSn1–xI3 films treated with DMAI maintain stable perovskite phases in air and exhibit improved optoelectronic properties. Devices fabricated with these films achieve power conversion efficiencies up to 14.2%, compared to 8.9% for untreated controls, and retain more than 94% of their initial performance after 3000 h of inert storage. This work highlights additive-driven stabilization as a pathway toward durable, high-efficiency all-inorganic perovskite solar cells.