A vertical antioxidant strategy for high performance wide band gap tin perovskite photovoltaics

Despite the promising characteristics of tin-based perovskite solar cells (TPSCs), one obvious limitation is the rapid oxidation of Sn2+, resulting in poor device performance and stability. Here, we introduced two different aromatic carboxylic acid molecules, 4,4 '-biphenyldicarboxylic acid (BP2Ac) and biphenyl-3,3 ',5,5 '-tetracarboxylic acid (BP4Ac), into the perovskite precursor solution, by adjusting pH of the precursor solution to suppress the fast Sn2+ oxidation. In addition, we proposed a vertical antioxidant strategy by simultaneously inhibiting the downward diffusion process of Sn4+ in both precursor solutions and perovskite films. Meanwhile, BP4Ac in the perovskite film can also form hydrogen bonds with the perovskite to further improve the stability of the device. Consequently, the unencapsulated devices retain nearly 87% of the initial PCE even after 1000 hours of storage in a nitrogen atmosphere. This strategy enabled the photovoltaic devices to deliver a power conversion efficiency of 10.35% with lower defect density. This work provides a novel antioxidant strategy for efficient wide band gap tin perovskite solar cells.