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

Abstract

Fullerene derivatives, such as C₆₀ 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 T₉₉ >1080 h under 85°C heating and T₉₉ >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.