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

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.