<i>In Situ</i> Engineered Gradient Ruddlesden–Popper 2D/3D Heterostructures at the Buried Interface Enable Current-Matched Perovskite/Silicon Tandems

In situ interface passivation serves as a crucial strategy for improving both the efficiency and stability of wide-band gap (WBG) perovskite solar cells and their associated tandem architectures. Here, we present a one-step in situ buried-interface passivation approach designed to reduce interface defects in three-dimensional (3D) WBG perovskite films. This is achieved by constructing self-assembly of a gradient Ruddlesden–Popper (RP) two-dimensional (2D) perovskite layer at the buried interface of the 3D WBG perovskite, leading to the formation of a gradient RP-2D/3D perovskite heterostructure. Such heterostructures facilitate the oriented growth of 3D perovskite crystals along the (100) plane, enhance charge carrier extraction, and effectively passivate trap states within the WBG perovskites. The in situ formation of RP-2D/3D perovskite heterostructures significantly enhances the light, thermal, and moisture stabilities of the WBG 3D perovskites. The resulting perovskite/silicon tandem solar cells exhibit improved current matching (mismatch 0.1% vs 5.5% for 3D), deliver improved efficiency of 32.73% (certified 32.46%), and demonstrate an operational lifetime T90 exceeding 1508 h.