2D perovskite as three-in-one interface modifier for efficient Pb-Sn perovskite solar cells and all-perovskite tandems

The performance of all-perovskite tandem solar cells (APTSCs) has been limited by narrow-band-gap lead-tin (Pb-Sn) perovskite sub-cells because of the uncontrollable crystallization and poor interface quality of Pb-Sn films, and a feasible strategy to comprehensively address these problems remains elusive. Herein, a two-dimensional (2D) 2-phenylethane-1-aminium lead iodide (PEA₂PbI₄) single crystal is demonstrated to serve as a “three-in-one” interface modifier, functioning as crystallization controller, buried seed, and capping passivator, to fabricate high-quality Pb-Sn films. The interaction between PEA₂PbI₄ and Pb-Sn perovskite promotes homogeneous nucleation and vertical crystal growth while strengthening both interfaces of the Pb-Sn films, enabling efficient charge transport and extraction. This three-in-one agent delivers Pb-Sn perovskite solar cells with an efficiency of 24.07% and T90 (time when efficiency dropped to 90%) over 2,000 h under ISOS-L-1. The constructed two-terminal APTSCs achieved an efficiency of 30.07% (certified 29.22%) with a fill factor (FF) of 84.77% and T90 over 1,800 h under ISOS-L-1.