Buried Interface Passivation of Sn–Pb Narrow‐Bandgap Perovskite for Highly Efficient All‐Perovskite Tandem Solar Cells

All‐perovskite tandem solar cells (ATSCs) present a remarkable opportunity to overcome the Shockley–Queisser efficiency limit of single‐junction solar cells. However, the stability of ATSCs significantly lags that of their pure Pb‐based single‐junction counterparts. Recent studies have identified that the widely used poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate) (PEDOT:PSS) hole transport layer in narrow‐bandgap (NBG) tin–lead (Sn–Pb) perovskite solar cells (PSCs) hinders the efficiency and stability. Herein, a patching strategy to optimize the interface between perovskite and PEDOT:PSS is proposed. Both theoretical and experimental studies reveal that PenA + and Ac − can decrease defect states at the interface and strengthen the binding between PEDOT:PSS and Sn–Pb perovskite. Furthermore, the pentylammonium acetate (PenAAc) interlayer improves carrier extraction and suppresses the oxidation of Sn 2+ to Sn 4+ . With the PenAAc buried layer, the fabricated NBG PSCs obtain an impressive power conversion efficiency (PCE) of 21.86%, along with significantly enhanced device stability. By integrating the buried passivated NBG Sn–Pb perovskite with a 1.75 eV wide‐bandgap PSC, the two‐terminal ATSC achieves a PCE of 26.54%. This work provides a valuable approach to fabricate efficient and stable NBG PSCs.