Nanostructured photoelectrodes with high surface area and tunable optical and electrical properties can potentially benefit a photoelectrochemical (PEC) water splitting system. PEC performance of a nanostructured photoelectrode is usually quantified in a standard three-electrode configuration under potential-assisted conditions because of the additional overpotentials for the two half-reactions of water splitting. However, it is a necessity to fully recognize their potential to split water under unassisted conditions by designing a tandem cell that can provide sufficient voltage to split water. Herein, we present a tandem cell comprised of a photocathode (e.g., carbon-modified cuprous oxide (C/Cu₂O) nanoneedles and MoS₂-coated Cu₂O) and a photoanode (e.g., Co modified BiVO₃and oxygen-deficient titanium dioxide (TiO_2−x) nanorods) for unassisted solar water splitting. The synthesized photoelectrodes were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and electrochemical impedance spectroscopy (EIS) techniques. The tandem cell performance was analyzed by measuring the current-voltage responses in various photoelectrode configurations to validate the collective contributions of both photoelectrodes to unassisted solar water splitting. The PEC properties of these paired photoanodes and photocathodes in a tandem configuration exhibited reasonable photocurrent in the absence of any redox mediator and external bias. Surface active species of photoanode are studied with an ultra-micro electrode of a scanning electrochemical microscope (SECM) to reveal the relationship to substrate and photoexcitation.