Optimization of high voltage-type solar cell comprising thin TiO2 on anode and thin Ag–TiO2 photocatalysts on cathode

Abstract A high-voltage type solar cell consisting of a TiO2 photocatalyst on the anode, an Ag–TiO2 photocatalyst on the cathode, and the water/O2 redox system is enabled and optimized by controlling the Ag size (~4 nm) and core–shell structure at the proximity of the indium tin oxide cathode, the photocatalyst film thickness (3.1 ± 0.3 μm), and the configuration of photoelectrodes in the solar cell (SC). The active sites for O2 photoreduction were Ag0 in situ formed on cathode irradiated by UV–visible light as evidenced by Ag K-edge extended X-ray absorption fine structure. Ag–Ag coordination number increased from 1.6 under aqueous HCl electrolyte to 9.6–11 under the conditions of SC tests, suggesting homogeneous Ag size distribution and maximized Ag0 active sites. The effective Ag0 shell was present only under the irradiation of UV–visible light; Ag0 sites were transformed into Ag2O sites when the light was turned off. By the optimization of Ag content and Ag–TiO2 film thickness on photocathode and light irradiation configuration from photocatalyst/electrode side on anode/cathode, an open-circuit voltage of 1.55 V exceeding most of the SC reported so far. Furthermore, cell power of 18.7 µW cm−2 was also achieved.