Additive Engineering Toward Suppression of Sn2+ Oxidation in Sn-Pb Perovskite Solar Cells: Mechanisms, Advances, and Outlook.

Inorganic hybrid tin-lead mixed perovskite solar cells (Sn-Pb PSCs) have attracted widespread attention in virtues of adjustable/narrow bandgaps, low toxicity, and application prospects in all-perovskite tandem solar cells, and the recorded power conversion efficiency (PCE) has reached 24.1%. However, the easy oxidation of Sn²⁺ brings about abundant Sn vacancies and high concentrations of p-type self-doping, leading to the efficiency and durability of Sn-Pb PSCs still lagging behind those of Pb-based counterparts. To inhibit the oxidation of Sn²⁺, feasible additive engineering is proposed and shows impressive effects. Herein, the recent research progress about additive engineering for Pb-Sn PSCs in depth is discussed and reviewed. The additive molecules are classified into antioxidant additives, reducing additives, and competitive additives, according to different action objects, namely Sn²⁺, Sn⁴⁺, and oxygen. Meanwhile, the corresponding functional groups, antioxidant properties, the effect on optoelectronic performances of the device, as well as underlying mechanisms are systematically summarized. Finally, an outlook is provided for future directions in additive engineering toward the suppression of Sn²⁺ oxidation in Sn-Pb perovskites.