The　performance　of　organic　photovoltaics　is　largely　dependent　on　the　balance　of　short-circuit　current　density　(JSC)　and　open-circuit　voltage　(VOC).　For　instance,　the　reduction　of　the　active　materials’　optical　bandgap,　which　increases　the　JSC,　would　inevitably　lead　to　a　concomitant　reduction　in　VOC.　Here,　we　demonstrate　that　careful　tuning　of　the　chemical　structure　of　photoactive　materials　can　enhance　both　JSC　and　VOC　simultaneously.　Non-fullerene　organic　photovoltaics　based　on　a　well-matched　materials　combination　exhibit　a　certified　high　power　conversion　efficiency　of　12.25%　on　a　device　area　of　1　cm2.　By　combining　Fourier-transform　photocurrent　spectroscopy　and　electroluminescence,　we　show　the　existence　of　a　low　but　non-negligible　charge　transfer　state　as　the　possible　origin　of　VOC　loss.　This　study　highlights　that　the　reduction　of　the　bandgap　to　improve　the　efficiency　requires　a　careful　materials　design　to　minimize　non-radiative　VOC　losses.　©　2018,　The　Author(s),　under　exclusive　licence　to　Springer　Nature　Limited.