A self-biasing photoelectrochemical (PEC) cell that could work for spontaneous overall water splitting in a neutral solution was established based on the mismatched Fermi levels between the photoelectrodes. A Pt-catalyst-decorated crystalline silicon photovoltaic cell (Pt/PVC) was prepared and employed as an effective photocathode. This was coupled with a poly(ethylene glycol)-directed WO3/W photoanode prepared by a hydrothermal process. Both of the photoelectrodes showed a response to visible light. The WO3/W photoanode had a positively located valence band edge, the energy level of which was enough for water oxidation, and the Pt/PVC photocathode possessed a negatively located conduction band edge, which was capable of water reduction. More importantly, the Fermi level of the WO3/W photoanode was more positive than that of the Pt/PVC photocathode because of the p–n junction of the PVC that decoupled the band bending and enlarged the photovoltage. Under visible-light irradiation, the WO3/W photoanode provided a negative bias for the Pt/PVC photocathode, and the Pt/PVC photocathode provided a positive bias for the WO3/W photoanode. An interior bias was generated that could relax the strict criteria of overall water splitting by cooperatively separating the hole–electron pairs at both photoelectrodes. In this system, the short-circuit current and the open-circuit voltage increased with increasing light intensity (AM 1.5 illumination) to reach 121 μA cm−2 and 0.541 V, respectively, at a light intensity of 100 mW cm−2. Such a combination provides a promising method for the fabrication of self-driven devices for solar-energy storage.