Dual Stress-Dissipation Pathways for Enhanced Thermomechanical Stability in Tin–Lead Perovskite Solar Cells

Substantial temperature fluctuations during device operation, coupled with the coefficient of thermal expansion (CTE) mismatch between the perovskite and substrate, generate significant thermal stress. This stress induces cracking in the perovskite film and interfacial delamination, severely compromising the stability of perovskite solar cells (PSCs). Nevertheless, this issue remains underexplored in tin–lead PSCs, where thermally induced mechanical failure is exacerbated by abundant stress concentration zones within the perovskite. Herein, we engineer dual stress-dissipation pathways by incorporating a poly[(prop-2-enamide)-co-(prop-2-enoic acid)] (PAA) copolymer. A pre-compressive stress established during film formation counteracts subsequent operational thermal tensile stresses. Concurrently, a flexible hydrogen-bonding network between PAA and perovskite provides an additional dissipation pathway, alleviating the stress concentration. Furthermore, PAA's flexible carbon chains enhance perovskite film flexibility and reduce CTE mismatch, thereby inhibiting thermally induced cracks and delamination. Consequently, PAA-optimized devices retain 85.0% of their initial efficiency after 1200 h of thermal cycling between 25 and 85 °C.