The Effect of Electronic Band Structure on High-Temperature Photovoltage Generation in CeO ₂ -Based Oxides

High-temperature photovoltage generation, driven by UV-enhanced oxygen incorporation, was investigated by using ionic conductive oxides with a fluorite-type structure. To elucidate the role of photoexcited electrons in this process, the UV photoresponse of CeO2 doped with various rare earth elements (Gd, La, Sm, Y, and Pr) and Y-doped ZrO2 was compared. Samples were irradiated with UV light at a central wavelength of 365 nm, and the open circuit voltage between the illuminated and nonilluminated surfaces was measured. A clear voltage increase, suggesting enhanced oxygen uptake, was observed in Gd-, La-, Sm-, and Y-doped CeO2, whereas Pr-doped CeO2 and Y-doped ZrO2 exhibited no increase. In Pr-doped CeO2, the Pr 4f band, located within the band gap, traps photoexcited electrons and accelerates electron–hole recombination. This mechanism prevents electrons and holes from participating in the reactions. In Y-doped ZrO2, the band gap is too large for UV excitation. These findings indicate that both the absence of impurity bands and the presence of UV absorption are essential for high-temperature photovoltage generation. This provides guidelines for discovering new materials and designing devices for solar-to-chemical energy conversion.