A narrow-band-gap molecular acceptor, IPIC-4Cl, featuring an indacenobis(dithieno[3,2-b:2′,3′-d]pyrrol) (INP) core with 2-butyl-1-octyl side chains and chlorinated (dicyanomethylidene)-indan-1-one (IC) as electron-accepting end group, has been rationally designed as nonfullerene acceptors (NFAs) for organic solar cells (OSCs). The impact of chlorination on the acceptor unit is revealed by a comparison study with two counterpart NFAs bearing a fluorinated or nonhalogenated IC unit. The synergetic photophysical and morphological analyses reveal that PBDB-T:IPIC-4Cl blend possesses efficient exciton dissociation and charge collection integrated with higher crystallinity and optimized phase separation. Consequently, the OSCs constructed by PBDB-T:IPIC-4Cl obtain a champion power conversion efficiency (PCE) of 13.4% with an extremely low energy loss of 0.51 eV. More encouragingly, we achieve a higher photovoltaic performance of 14.3% for ternary solar cells by combining an optimal amount of PC71BM with PBDB-T:IPIC-4Cl blend.