Hot‐Carrier Cooling Regulation for Mixed Sn‐Pb Perovskite Solar Cells

Abstract The rapid relaxation of hot carriers leads to energy loss in the form of heat and consequently restricts the theoretical efficiency of single‐junction solar cells; However, this issue has not received much attention in tin‐lead perovskites solar cells. Herein, tin(II) oxalate (SnC₂O₄) is introduced into tin‐lead perovskite precursor solution to regulate hot‐carrier cooling dynamics. The addition of SnC₂O₄ increases the length of carrier diffusion, extends the lifetime of carriers, and simultaneously slows down the cooling rate of carriers. Furthermore, SnC₂O₄ can bond with uncoordinated Sn²⁺ and Pb²⁺ ions to regulate the crystallization of perovskite and enable large grains. The strongly reducing properties of the C₂O₄²⁻ can inhibit the oxidation of Sn²⁺ to Sn⁴⁺ and minimize the formation of Sn vacancies in the resulting perovskite films. Additionally, as a substitute for tin(II) fluoride, the introduction of SnC₂O₄ avoids the carrier transport issues caused by the aggregation of F^– ions at the interface. As a result, the SnC₂O₄‐treated Sn‐Pb cells show a champion efficiency of 23.36%, as well as 27.56% for the all‐perovskite tandem solar cells. Moreover, the SnC₂O₄‐treated devices show excellent long‐term stability. This finding is expected to pave the way toward stable and highly efficient all‐perovskite tandem solar cells.