The widespread use of Internet-of-things (IoT) devices has inspired researchers to adopt unique material design strategies to realize efficient indoor organic photovoltaic (OPV) systems. However, despite acceptor halogenation being an effective strategy for modulating OPV properties, studies on the systematic examination of nonfullerene acceptor- (NFA-) OPVs under dim indoor light using the halogenation approach are scarce. This study evaluates the performance of NFA-OPVs under indoor light by employing a halogenation approach with Y6-derivatives. The choice of the chlorination or fluorination unit in an NFA significantly affects the indoor performance of OPVs. The champion OPV devices with a chlorinated acceptor demonstrated excellent power conversion efficiency (PCE) of 25.5% compared to that of the fluorinated acceptor (PCE: 22.5%) under 1000-lx light-emitting-diode (LED) illumination. Moreover, suitable energy levels, satisfactory spectral matching, and improved surface morphology of the chlorinated acceptors resulted in the excellent indoor performance of the OPVs. In addition, acceptor chlorination resulted in high crystallinity and planarity, which facilitated suppressed trap-assisted recombination and low open-circuit voltage (VOC) loss of OPV devices in an indoor environment.