Abstract: Reduced graphene oxide (RGO) with various mass percent (0.4, 0.8, 1.2, 1.6, 2.0 and 2.4 wt.%) was incorporated into Cu₄Bi₄S₉ to fabricate different composites (CBS-RGO). With ZnO nanowires as electron acceptor, CBS-RGO (or CBS nanoribbons) as electron donor, two types of heterojunctions (ZnO/CBS and ZnO/CBS-RGO), as well as bulk heterojunction (BHJ) solar cells were studied in detail. RGO from 0.4 to 1.6 wt.%, the surface photovoltage (SPV) of CBS-RGO increased gradually. There is the highest SPV at RGO of 1.6 wt.%. However, the SPV decreased continuously with RGO in excess 1.6 wt.%. Here, ZnO/CBS-RGO exhibits the higher photovoltaic response than that of ZnO/CBS. Under the same positive bias, ZnO/CBS-RGO also presents the more excellent SPV than that of ZnO/CBS. With the bias increasing, the SPV of ZnO/CBS-RGO improved very quickly. Based on RGO of 1.6 wt.%, two types of BHJ solar cells of ZnO/CBS and ZnO/CBS-RGO exhibit the highest photoelectric conversion efficiencies of 1.5% and 3.6%, respectively. From thickness of film, energy level matching, contact interface of CBS and RGO, RGO conductive network, as well as RGO remarkably high electron mobility, the separation mechanism of photogenerated charges and the effect of multichannel improved transport were analysed in BHJ.