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.