Two low band-gap donors, small molecule p-DTS(FBTTh2)(2) (S-D) and polymer PBDTTT-C-T (P-D), and two perylene diimide acceptors, small molecule PDI-2DTT (S-A) and polymer PPDIDTT (P-A), were used to fabricate non-fullerene organic solar cells. The effects of four donor/acceptor combinations, P-D/P-A, P-D/S-A, S-D/S-A and S-D/P-A, on the morphology, charge transfer, charge transport and photovoltaic performance were investigated. Power conversion efficiencies (PCEs) of P-D/P-A, P-D/S-A, S-D/S-A and S-D/P-A were 3.04%, 0.28%, 2.52% and 0.29%, respectively. The P-D/P-A blend and S-D/S-A blend exhibited relatively uniform and continuous morphology, efficient photoinduced charge transfer, high mobility and balanced charge transport relative to P-D/S-A and S-D/P-A blends, leading to much higher PCEs.