Purification of Tin Iodide through Solid-State Reaction for Efficient Tin-Lead Mixed Perovskite Solar Cells

Tin-lead (Sn-Pb) mixed perovskite solar cells (PSCs), which serve as the rear subcell, have achieved significant advancements, largely driving the remarkable power conversion efficiency (PCE) seen in recent all-perovskite tandem solar cells (TSCs). However, the efficiency of Sn-Pb mixed PSCs is limited by the oxidation susceptibility of Sn²⁺, which induces the formation of Sn vacancies in the perovskite thin films, leading to an increase in defect densities. To address this issue, a novel approach called metal-assisted solid-state reduction (MASSR) is introduced that effectively purifies tin iodide (SnI₂), a critical component in the fabrication of Sn-Pb mixed perovskite thin films. The MASSR process controls the oxidation state of the SnI₂, thereby reducing trap densities and minimizing non-radiative recombination losses in the perovskite thin films, which improves the overall efficiency of Sn-Pb mixed PSCs. Consequently, single-junction Sn-Pb mixed PSCs utilizing MASSR-treated SnI₂ achieve a high PCE of 22.86%, and their integration with wide-bandgap (WBG) PSCs enables the fabrication of all-perovskite TSCs with a PCE of 26.88%.