Highly Efficient Tin Perovskite Solar Cells via Suppressing Superoxide Generation

Power conversion efficiency (PCE) and stability of tin perovskite solar cells (TPSCs) are major concerns in developing lead-free photovoltaics. Photovoltaic performance of TPSCs often suffers from the oxidation of Sn2+, organic degradation, and ion migration, which inevitably cause plenty of trap states and render inferior device parameters. Herein, a natural ascorbic acid is first introduced for high-performance TPSCs as a multifunctional reductant to suppress the oxidation of Sn2+ and regulate trap states accordingly. Interestingly, it is found that the ascorbic acid reduces Sn4+ to Sn2+ by C=C double bonds and forms a complex with Cs(0)(.0)(5)FA(0)(.9)(5)SnI(3) perovskites via strong hydrogen bonding interactions. By virtue of theoretical calculations, the mechanism of the ascorbic acid role is further clarified. Apart from effective passivation and suppressing trap density, a superoxide interaction between perovskite and ascorbic acid is proposed. The existence of ascorbic acid successfully improved the energy barrier for O-2(-) generation. As a result, a significantly improved PCE from 8.95% to 13.32% is achieved for Cs(0.05)FA(0.95)SnI(3) TPSCs with 0.5% ascorbic acid incorporation under AM 1.5 G illumination. In addition, our devices maintain 90% value of initial PCE after 500 h storage.