We describe a ternary photoactive layer based on PffBT4T-2OD as a donor with a blend of dihydronaphthyl-based C60 bisadduct (NCBA) and PC71BM as the acceptor. It offers ideal exciton dissociation, an ideal charge-carrier recombination and photovoltaic performance relationship, and improves the power-conversion efficiency (PCE) and stability of polymer solar cells (PSCs). NCBA has a broad visible-light absorption spectrum and shallower lowest unoccupied molecular orbital (LUMO) energy levels, which enhance exciton dissociation and charge-carrier transport and suppress charge-carrier recombination. This remarkably increases the photocurrent density and fill factor. An optimized PCE of 9.79% was achieved for the ternary PffBT4T-2OD:NCBA:PC71BM(1:0.24:0.96)-based PSCs. The mechanism was exciton dissociation at the PffBT4T-2OD/NCBA, PffBT4T-2OD:PC71BM, and NCBA/PC71BM interfaces. This simultaneously enhances the exciton-dissociation ratio and charge-carrier transport. Meanwhile, PSCs with 20% NCBA as third-component materials exhibit improved thermal stability and photo-stability leading to a lower ratio of PCE under long-time thermal-annealing and visible-light-illuminated treatment. This work indicates that NCBAs are third-component materials that significantly improve PSC performance.