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., EDAI2 and EDABr2) as additives in Sn perovskite and find that both EDAI2 and EDABr2 can suppress Sn oxidation and passivate trap states, however, EDABr2 works better than EDAI2 in terms of passivating undesired grain boundaries and surface Sn vacancies, and reducing background hole density, due to the synergistic roles of EDA2+ cation and Br- anion. Moreover, EDABr2 exhibits more consummate passivation effect on SnI 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 EDABr2-modified device achieves a power conversion efficiency of 14.23% with long-term durability of keeping ∼93% of its initial efficiency after storing for ∼4000 h and improved operational stability. Our work provides a promising approach to choose satisfactory passivators and fabricate efficient Sn perovskite solar cells.