Efficient Sn–Pb Mixed Perovskite Solar Cells Via Minimizing Solvent Oxidation

Abstract Tin (Sn)–lead (Pb) mixed perovskite solar cells (PSCs) stand out as the optimal choice for the bottom subcell of the all‐perovskite tandem solar cells. One of the major challenges impeding the further enhancement of Sn–Pb mixed PSCs power conversion efficiency (PCE) is the easy oxidation of Sn²⁺ to Sn⁴⁺ and a large number of Sn vacancies in the perovskite films. In this work, the sources of Sn²⁺ oxidation in the perovskite precursor solution are systematically investigated, focusing on the oxidation state of raw materials, solvent‐dissolved oxygen, and solvent oxidizing ability. It is discovered that compared to the commonly used dimethyl sulfoxide (DMSO) solvent, N, N'‐Dimethylpropyleneurea (DMPU) exhibits a weaker oxidizing ability while forming excellent coordination with the perovskite precursor. Using a mixed solvent of N, N‐Dimethylformamide (DMF), and DMPU as the precursor solvent not only obviates the need for additional antioxidants but also demonstrates reduced oxidation susceptibility toward Sn–Pb mixed perovskite. Utilizing a gas‐assisted technique without anti‐solvents, high‐efficiency Sn–Pb mixed PSCs are fabricated. These findings not only deepen the understanding of the oxidation phenomena in Sn–Pb perovskite precursor solutions but also provide essential guidance for the scalable production of Sn–Pb mixed PSCs and tandem solar cells.