Regulating crystallization and retarding oxidation in Sn-Pb perovskite via 1D cation engineering for high performance all-perovskite tandem solar cells

All-perovskite tandem solar cells have the potential to surpass the theoretical efficiency limit of single junction solar cells by reducing thermalization losses. However, the challenges encompass the oxidation of Sn²⁺ to Sn⁴⁺ and uncontrolled crystallization kinetics in Sn-Pb perovskites, leading to nonradiative recombination and compositional heterogeneity to decrease photovoltaic efficiency and operational stability. Herein, we introduced an ionic liquid additive, 1-ethyl-3-methylimidazolium iodide (EMIMI) into Sn-Pb perovskite precursor to form low-dimensional Sn-rich/pure-Sn perovskites at grain boundaries, which mitigates oxidation of Sn²⁺ to Sn⁴⁺ and regulates the film-forming dynamics of Sn/Pb-based perovskite films. The optimized single-junction Sn-Pb perovskite devices incorporating EMIMI achieved a high efficiency of 22.87%. Furthermore, combined with wide-bandgap perovskite sub-cells in tandem device, we demonstrate 2-terminal all-perovskite tandem solar cells with a power conversion efficiency of 28.34%, achieving improved operational stability.