Near-Infrared Fully Nonfused Acceptors with Selenophene Central Core and Halogenated End-Groups for Efficient Organic Solar Cells

Two fully nonfused electron acceptors (FNEAs) were developed, comprising a selenophene central core flanked by halogenated end-groups (fluorine and chlorine derivatives), to probe the structure–property relationships. The chlorinated 4TSe-Cl exhibits a red-shifted absorption and enhanced crystallinity compared with its fluorinated counterpart (4TSe-F). When paired with polymer donor D18, the 4TSe-Cl-based devices delivered a champion power conversion efficiency (PCE) of 13.74%, surpassing those devices based on D18/4TSe-F (12.96%), which is among the best in FNEA-based devices. The superior performance of 4TSe-Cl can be attributed to its better miscibility with D18, formation of a more refined fibrillar-like network structure, improved charge transport properties, and higher carrier mobility in the blend. This work highlights that synergistic modulation of both the central core and end-groups in nonfused electron acceptors is a promising approach toward achieving high-efficiency organic solar cells (OSCs).