Dual‐Stage Reduction Strategy of Tin Perovskite Enables High Performance Photovoltaics

The rapid oxidation of Sn2+ in tin‐based perovskite solar cells (TPSCs) restricts their efficiency and stability have been main bottleneck towards further development. This study developed a novel strategy which utilizes thiosulfate ions (S2O32‐) in the precursor solution to enable a dual‐stage reduction process. In the solution stage, thiosulfate acted as an efficacious reducing agent to reduce Sn4+ to Sn2+, meanwhile, its oxidation products were able to reduce I2 to I‐ during the film stage. This dual reduction ability effectively inhibited the oxidation of Sn2+ and passivated defects, further promising an excellent stability of the perovskite devices. As a result, thiosulfate‐incorporated devices achieved a high efficiency of 14.78% with open‐circuit voltage reaching 0.96 V. The stability of the optimized devices achieved a remarkable improvement, maintaining 90% of their initial efficiencies after 628 hours at maximum‐power‐point (MPP). The findings provid research insights and experimental data support for the sustained dynamic reduction in TPSCs.