Selenopheno[3,2-b]thiophene-Based Narrow-Bandgap Nonfullerene Acceptor Enabling 13.3% Efficiency for Organic Solar Cells with Thickness-Insensitive Feature

A new electron-rich central core (SeT) based on a fused selenopheno[3,2-b]thiophene unit and two nonfullerene small-molecule acceptors is synthesized for organic solar cells. Compared with SeTIC, chlorinated SeTIC4Cl exhibits a stronger near-infrared absorption with a smaller bandgap (1.44 eV), down-shifted highest occupied molecular orbital/lowest unoccupied molecular orbital energy levels, and improved crystallinity with higher electron mobility owing to the stronger intramolecular charge-transfer effect. Therefore, SeTIC4Cl/PM6 blend films exhibited significantly higher power conversion efficiency owing to broader light absorption range, more balanced charge mobility, and desirable nanoscale phase separation for exciton dissociation and reduced geminate recombination. As a result, the optimized device based on SeTIC4Cl/PM6 shows a higher power conversion efficiency (PCE) of 13.32%, which is the highest value to date for selenophene-containing nonfullerene acceptor (NFA)-based binary organic solar cells. Equally important, the PCE of SeTIC4Cl is insensitive to the variation in thickness of the active layer to 300 nm. Our results demonstrate the great potential of the selenopheno[3,2-b]thiophene unit for designing high-performance NFAs.