Molecular Coordination–Driven Photothermally Stable FACs‐based Perovskite Solar Cells with Efficiency Over 25% via Dicarbonyl‐Functionalized Thienoacene Small Molecule

ABSTRACT The practical deployment of perovskite solar cells (PSCs) is critically hindered by their susceptibility to moisture, oxygen, and thermal degradation, particularly under high‐temperature and high‐humidity conditions. Herein, we design and synthesize a dicarbonyl‐functionalized thienoacene passivator featuring multiple Lewis basic sites and medium‐length heptyl chains. This molecule exhibits exceptional thermal stability and anchors robustly at perovskite grain boundaries via multidentate Pb─O and Pb─S coordination bonds, effectively relieving interfacial tensile strain, passivating electronic defects, and enhancing the thermal integrity of the perovskite lattice. The hydrophobic heptyl chains further impart superior moisture resistance, while the π ‐conjugated backbone facilitates efficient charge transfer at the perovskite/hole‐transport layer interface. As a result, the target devices achieve a champion power conversion efficiency of 25.02% for lab‐scale cells and 23.34% for 1.0 cm 2 devices. Notably, the unencapsulated devices retain over 82% of their initial efficiency after 1000 h of continuous illumination at 85°C under an inert atmosphere. This work establishes multidentate surface passivation and strain management as a highly effective strategy for realizing efficient and operationally stable perovskite photovoltaics.