Dual-site passivation of tin-related defects enabling efficient lead-free tin perovskite solar cells

Tin (Sn) perovskites as photovoltaic materials show great promise due to their suitable bandgaps and lower toxicity. However, various defects in Sn perovskites induce significant losses in devices. In this work, we report a strategy of dual-site passivation of Sn-related defects in lead-free Sn perovskite solar cells. We adopt ethylenediammonium halide salts (i.e., EDAI(2) and EDABr(2)) as additives in Sn perovskite and find that both EDAI(2) and EDABr(2) can suppress Sn oxidation and passivate trap states, however, EDABr(2) works better than EDAI(2) in terms of passivating undesired grain boundaries and surface Sn vacancies, and reducing background hole density, due to the synergistic roles of EDA(2+) cation and Br- anion. Moreover, EDABr(2) exhibits more consummate passivation effect on Sn-I antisite defects as deep-level traps due to its larger electrostatic potential and shorter bonding length between -Br and -Sn. These enable great suppression of non-radiative recombination and enhancement of charge carrier transport. As a result, the best-performing EDABr(2)-modified device achieves a power conversion efficiency of 14.23% with long-term durability of keeping similar to 93% of its initial efficiency after storing for similar to 4000 h and improved operational stability. Our work provides a promising approach to choose satisfactory passivators and fabricate efficient Sn perovskite solar cells.