Synthesis of Stable SnI₂·xDMSO Adducts toward Efficient Tin-Lead Perovskite Solar Cells

Sn-Pb narrow-bandgap perovskites are indispensable for achieving highly efficient all-perovskite tandem solar cells as bottom subcells. However, facile oxidation of Sn²⁺ into Sn⁴⁺ leads to the poor precursor stability, which largely hinders the development of Sn-Pb perovskite solar cells (PSCs). Herein, we present a novel strategy to synthesize SnI₂·xDMSO intermedium adducts in situ utilizing a mild one-to-one reaction between molecular SnI₄ and metallic Sn. This approach avoids the formation of low-coordinated SnI₂·xDMSO clusters (x ≤ 2), yielding highly coordinated SnI₂·xDMSO (x = 3) adducts with enhanced antioxidation ability. The resultant precursor showed outstanding stability and reproducibility. The aged precursor for 7 days maintains its initial properties. Consequently, the resulting Sn-Pb PSCs deliver an impressive efficiency of 22.64% and retain ∼ 90% of their initial value after maximum power point operation under simulated one-sun illumination in air for 530 h under encapsulation. Our finding provides an effective pathway to enhance the intrinsic antioxidant capacity of Sn²⁺ in perovskite precursors, paving a way for the development of efficient and reproducible Sn-Pb PSCs.