Origin of Ultraviolet‐Induced High‐Temperature Photovoltaic Response at Pt/Gd‐Doped CeO ₂ Interface

Abstract This study investigates the ultraviolet (UV) response of 10 mol.% gadolinium‐doped ceria (CGO) at elevated temperatures, a key property for its application in emerging solid oxide high‐temperature photoelectrochemical cells – an innovative class of solar energy conversion device. Dense CGO pellets with platinum electrodes on both sides are prepared, and one side is irradiated with UV light ( λ = 365 nm). The origin of the UV‐induced open‐circuit voltage is investigated. UV‐induced open‐circuit voltage ( V OC ) increases with the oxygen (O 2 ) concentration in the flow gas, reaching up to 90 mV at 400 °C in 100% O 2 , while no voltage is detected in a hydrogen atmosphere. Under conditions where a UV response in V OC is present, impedance measurements reveal a decrease in resistance and an increase in capacitance of the low‐frequency element. Current–voltage measurements also showed enhanced cathodic current. Furthermore, UV irradiation on one side of the pellet increases the O 2 concentration on the opposite side. These results demonstrate that UV exposure at the Pt/CGO interface promotes oxygen uptake, modifies the oxygen nonstoichiometry at the irradiated surface, and induces an oxygen chemical potential gradient across the thickness of the CGO pellet, providing new insight into photoinduced ionics in high‐temperature solid‐state devices.