Sol-gel synthesis and thermoelectric properties of AZO films with pyrolytic carbon inclusions

We report on our measurements of the thermoelectric properties, including the Seebeck coefficient, electrical conductivity, thermal conductivity, power factor, and dimensionless thermoelectric figure of merit (ZT), at room temperature, in various sol-gel prepared films of Al-doped ZnO with as prepared Al to Zn molar ratios ranging from 0% to 10%. As a result of the sol-gel processing, these films have C-based impurities that affect both their thermal and electrical properties. While normally considered an unwanted feature, these C inclusions could be engineered and used to modify the properties of the Al-ZnO system for certain applications. Our samples showed, for Al contents smaller than 1%, an apparently strong electron contribution to the thermal conductivity despite the low observed electrical conductivity, and a roughly constant ratio of the thermal to electrical conductivity (Lorenz number)−1 as a function of Al content up to ∼ 2%. We believe that this metallic character may be a result of increased phonon scattering due to C inclusions and grain-boundary scattering.