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

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 C₂O₄ ^2- 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.