Dual-Site Anchors Enabling Vertical Molecular Orientation for Efficient All-Perovskite Tandem Solar Cells

All-perovskite tandem solar cells (TSCs) are gaining increasing attention due to their potential to surpass the efficiency limit of single-junction solar cells. However, as the bottom low-bandgap subcells, tin-lead (Sn-Pb) perovskites suffer from severe nonradiative recombination at the interfaces due to their susceptibility to oxidation and poor crystalline morphology. Here a surface modifier 4-(trifluoromethyl)benzhydrazide (TFH) is reported to construct a reductive chemical environment on the surface of perovskite films and protect them from water and oxygen erosion. TFH anchors onto the Sn-Pb perovskites in a preferred vertical orientation through dual-site binding, forming interface dipoles that facilitate charge extraction. The reductive hydrazine groups of TFH can effectively inhibit the oxidation of Sn²⁺ and I⁻, thereby reducing the defect density and energy disorder of Sn─Pb perovskites. Consequently, the TFH-treated devices achieved a champion PCE of 22.88%, maintaining over 93% of the initial efficiency after continuous one-sun illumination for 500 h. Combined with a 1.79 eV wide-bandgap subcell, it has demonstrated a PCE of 28.17% in all-perovskite TSCs.