n-Type polymer layers enable efficient, scalable, and thermally stable perovskite solar modules

Fullerene-based electron transport layers (ETLs) used in inverted (p-i-n) perovskite solar cells face issues regarding cost, scalability, and instability, whereas highly stable inorganic oxides feature unfavorable energy alignment and enhance hysteresis, which reduce power conversion efficiency (PCE). We report a nonfullerene conjugated polymer, 2PB-T, that incorporates coplanar and electron-withdrawing perylene bisimide (PBI) units into its backbone. The PBI polymeric backbone and side-chain engineering address the instability of small-molecule ETLs by optimizing electron transport properties, film uniformity, and interfacial binding. Small-area devices achieved a champion PCE of 27.8%, with a certified maximum power point tracking (MPPT) efficiency of 27.3%. Perovskite modules with areas of 20.6 and 625 square centimeters reached PCEs of 24.4 and 22.5%, respectively. Small-area devices retained more than 98.6% of their initial PCE after 1752 hours of continuous MPPT at 85°C in air, and the 625-square-centimeter module maintained 96.9% of its initial PCE after 5900 hours of outdoor operation.