State-of-the-art　organic　solar　cells　(OSCs)　typically　suffer　from　large　voltage　loss　(V＜sub＞loss＜/sub＞　)　compared　to　their　inorganic　and　perovskite　counterparts.　There　are　some　successful　attempts　to　reduce　the　V＜sub＞loss＜/sub＞　by　decreasing　the　energy　offsets　between　the　donor　and　acceptor　materials,　and　the　OSC　community　has　demonstrated　efficient　systems　with　either　small　highest　occupied　molecular　orbital　(HOMO)　offset　or　negligible　lowest　unoccupied　molecular　orbital　(LUMO)　offset　between　donors　and　acceptors.　However,　efficient　OSCs　based　on　a　donor/acceptor　system　with　both　small　HOMO　and　LUMO　offsets　have　not　been　demonstrated　simultaneously.　In　this　work,　an　efficient　nonfullerene　OSC　is　reported　based　on　a　donor　polymer　named　PffBT2T-TT　and　a　small-molecular　acceptor　(O-IDTBR),　which　have　identical　bandgaps　and　close　energy　levels.　The　Fourier-transform　photocurrent　spectroscopy　external　quantum　efficiency　(FTPS-EQE)　spectrum　of　the　blend　overlaps　with　those　of　neat　PffBT2T-TT　and　O-IDTBR,　indicating　the　small　driving　forces　for　both　hole　and　electron　transfer.　Meanwhile,　the　OSCs　exhibit　a　high　electroluminescence　quantum　efficiency　(EQE＜sub＞EL＜/sub＞　)　of　≈1　×　10＜sup＞-4＜/sup＞　,　which　leads　to　a　significantly　minimized　nonradiative　V＜sub＞loss＜/sub＞　of　0.24　V.　Despite　the　small　driving　forces　and　a　low　V＜sub＞loss＜/sub＞　,　a　maximum　EQE　of　67%　and　a　high　power　conversion　efficiency　of　10.4%　can　still　be　achieved.