A Mixed PC₆₁BM-COi8DFIC Based Electron Transport Material for Inverted High-performance Perovskite Solar Cells

This study reports a blend of [6, 6]-phenyl-C61-butyric acid methyl ester (PC₆₁BM) and COi8DFIC non-fullerene acceptor (NFA) as an electron transport layer (ETL) in perovskite solar cells (PSCs). This mixed small-molecule ETL showed good inter-molecule mixing, reduced intermolecular distances and decent morphology, resulting in excellent charge carrier transport properties. Morever, charge carrier extraction and transport at the perovskite/ETL interface was optimized by reducing surface traps and defects due to the passivation ability of various terminal groups from the COi8DFIC molecule. A high power conversion efficiency (PCE) of 19.12 % was achieved by taking advantage of benefits from both molecules, showing much better performance than the invidual PC₆₁BM or COi8DFIC (7.13% for using the NFA only). Moreover, the storage and ambient stabilities of the mixed ETL-based PSCs increased dramatically compared to control devices.