ICT2014 Abstracts

We focused on the controls of Seebeck coefficient (S) and electrical conductivity (s) of tungsten trioxide (WO₃) by light. Here, a sputtered crystalline WO₃ thin film generated thermoelectric power due to ultraviolet (UV) light-induced band-gap excitation and was accompanied by a photochromic reaction resulting from generating W⁵⁺ ions. The s and S values and coloration of WO₃ could be reversibly switched by alternating the external stimulus between UV light irradiation and dark storage. After irradiating with UV light, s increased, whereas the absolute value of S decreased, and the photochromic (coloration) reaction was observed. The opposite behavior was exhibited by WO₃ after dark storage, and this reversible cycle could be repeated at least three times. The photo-conductivity (s_photo) and photo-Seebeck coefficient (S_photo) were also detected in response to visible-light irradiation of the colored WO₃ thin films. While irradiating visible light, s_photo and the absolute value of S_photo increased and decreased, respectively. These effects are likely attributable to the excitation of electrons from the mid-gap visible light absorption band (W⁵⁺ state) to the conduction band of WO₃.