Halogenated Nonfused Ring Electron Acceptor for Organic Solar Cells with a Record Efficiency of over 17%

Abstract Three nonfused ring electron acceptors (NFREAs), namely, 3TT‐C2‐F, 3TT‐C2‐Cl, and 3TT‐C2, are purposefully designed and synthesized with the concept of halogenation. The incorporation of F or/and Cl atoms into the molecular structure (3TT‐C2‐F and 3TT‐C2‐Cl) enhances the π–π stacking, improves electron mobility, and regulates the nanofiber morphology of blend films, thus facilitating the exciton dissociation and charge transport. In particular, blend films based on D18:3TT‐C2‐F demonstrate a high charge mobility, an extended exciton diffusion distance, and a well‐formed nanofiber network. These factors contribute to devices with a remarkable power conversion efficiency of 17.19%, surpassing that of 3TT‐C2‐Cl (16.17%) and 3TT‐C2 (15.42%). To the best of knowledge, this represents the highest efficiency achieved in NFREA‐based devices up to now. These results highlight the potential of halogenation in NFREAs as a promising approach to enhance the performance of organic solar cells.