Multifunctional Oriented Dipole Strategy for Synergistic Energy‐Level Alignment and Defect Passivation at Buried Interfaces Toward 29.5%‐Efficient All‐Perovskite Tandem Solar Cells

ABSTRACT All‐perovskite tandem solar cells promise to surpass the Shockley–Queisser limit, but the buried interface between the hole transport layer (HTL) and narrow‐bandgap (NBG) Pb–Sn perovskite suffers from non‑radiative recombination, energy mismatch, and defects. Here, we use 3‑amino‑4‑hydroxybenzenesulfonic acid (APS) as a multifunctional dipolar molecule to engineer this interface. The sulfonate group anchors onto the HTL, creating oriented dipoles that tailor the electrostatic field; amino and hydroxyl groups synergistically passivate traps, coordinate undercoordinated Pb 2 + and Sn 2 + , inhibit Sn 2 + oxidation, and modulate crystallization. This optimizes energy alignment, establishes a type‑II band structure and ohmic contact, suppresses recombination, and promotes carrier transport. Consequently, the APS‑modified single‑junction NBG Pb–Sn cell achieves a power conversion efficiency (PCE) of 24.02%, versus 22.21% for the control, and shows improved stability (retaining 86% of initial PCE after 2600 h in N 2 ). Applying the same strategy to all‑perovskite tandem cells yields a PCE of 29.51%. This work provides a dipole‑mediated interface design that simultaneously addresses defect passivation, energy‑level tuning, and charge extraction, offering a promising pathway toward high‑efficiency and durable Pb–Sn mixed perovskite solar cells and their tandem architectures.