Molecular Engineering of Electron Transport Layers via Steric Hindrance and Chelation Toward Stable Inverted Perovskite Solar Cells

ABSTRACT Fullerene derivatives, such as C 60 and PCBM, are widely used as electron transport layers (ETLs) in inverted perovskite solar cells (PSCs) due to their high electron mobility and well‐aligned energy levels. However, their poor photo‐thermal stability and weak interactions with perovskite limit further progress. To address these challenges, we develop a novel fullerene derivative, 2Py, as the ETL for inverted PSCs via a synergistic strategy combining steric hindrance modulation and chelation group incorporation. This molecule delivers three key benefits: moderate steric hindrance inhibits ETL aggregation during thermal aging; chelation groups enhance interfacial interactions with the perovskite layer; and improved hydrophilicity promotes uniform SnO x film growth via atomic layer deposition (ALD). 2Py ETL enables an efficiency of 26.07% for inverted PSCs based on a 1.55‐eV bandgap. Wide‐bandgap (1.80 eV) and narrow‐bandgap (1.25 eV) PSCs achieve efficiencies of 19.94% and 24.06%, respectively. Notably, these devices demonstrate exceptional photo‐thermal stability, achieving T 99 >1080 h under 85°C heating and T 99 >1250 h under maximum power point tracking at 45°C, outperforming PCBM‐based devices. This molecular design strategy paves new pathways for enhancing ETL performance and stability in inverted PSCs.