In this work, we have firstly proposed a mild and facile method to deposit large-area RGO and ZnO QDs/RGO films on diverse substrates through a self-assembly strategy. RGO powders would aggregate to agglomerate in aqueous solution due to its hydrophobicity. Interestingly, it is found that RGO sheets would assemble to film when RGO ethanol solution is dropped into water, and the film layers could be rationally tuned by repeating the deposition procedure. Based on the convenient fabrication method, a co-current Z-scheme system could be constructed by subsequently depositing RGO and ZnO QDs/RGO films on FeVO4 photoelectrodes, in which RGO serves as an electron mediator. Different from the traditional disordered Z-scheme system, the photo-excited electrons in co-current Z-scheme would move toward the same direction due to the absolute separation between FeVO4 and ZnO. As a result, the PEC performances of FeVO4 could be significantly enhanced because the running direction of photo-excited electrons in co-current Z-scheme is consistent with that in external circuit. For comparison, a counter-current Z-scheme has also been built up by replacing FeVO4 with WO3, in which the ruing direction of photo-generated electrons is opposite to the external circuit, and the photo conversion efficiency decreased consequently. Therefore, it can be concluded that the design of pure Z-scheme is not only beneficial for improving the charge separation efficiency and retaining their redox capability, but also favorable for uncovering the charge transfer mechanism.