Bidentate Phosphonate Bridges Enable Buried Interface Reconstruction for Thermomechanically Robust Sn–Pb Perovskite Solar Cells

ABSTRACT Tin–lead (Sn–Pb) mixed perovskite solar cells (PSCs) are promising for high‐efficiency tandem photovoltaics. However, substantial temperature fluctuations during device operation generate mechanical stresses that, coupled with insufficient adhesion at the perovskite/hole transport layer (HTL) interface, induce perovskite cracking and interfacial delamination. These structural degradations hinder efficient hole extraction and compromise long‐term device stability. In this study, we introduce 1,2‐ethylenediphosphonic acid (EDPA) as an interfacial molecular bridge to reconstruct the contact interface between the perovskite and HTL. The terminal phosphonic acid groups of EDPA simultaneously anchored to poly(3,4‐ethylenedioxythiophene)(styrenesulfonate) (PEDOT:PSS) and coordinated with B‐site metal ions in the perovskite, enhancing interfacial adhesion and generating pre‐compressive stress during film formation, effectively counteracting thermally induced tensile stress during device operation. Concurrently, EDPA disrupts the intrinsic electrostatic interactions within HTL via hydrogen‐bonding interactions, facilitating the segregation of insulating PSS chains, exposing the conductive PEDOT network, and reconstructing a more efficient hole‑extraction interface. Given these synergistic mechanical and electrical enhancements, the optimized PSC achieves a 23.96% power conversion efficiency (PCE), retaining 90.4% of its initial efficiency after 1200 h of thermal cycling (25°C–85°C). This study establishes a buried‐interface reconstruction strategy for realizing thermomechanically robust Sn–Pb perovskite photovoltaics under practical operating conditions.