Transparent niobium-doped titanium dioxide thin films with high Seebeck coefficient for thermoelectric applications

Abstract

This work reports the production and characterization of optically transparent Nb-doped TiO2 thin films with enhanced thermoelectric properties deposited on glass and Si by reactive d.c. magnetron sputtering in high vacuum. The purpose of these films is to harvest thermal energy from the environment and convert it to electrical energy. Several process parameters, such as reactive and working gas flow rate, deposition temperature, target current density and post-annealing conditions, directly affect the morphology and crystalline structure of the thin films. The optimization of these parameters results in thin films with thickness of 120–300 nm, maximum average optical transmittance in the visible range of 73%, n-type electrical resistivity of 0.05 Ω·cm, thermal conductivity around 1.5 W·m−1·K−1 and a maximum absolute Seebeck coefficient of 223 μV·K−1. The resulting maximum thermoelectric power factor is 60 μW·K−2·m−1 and the maximum thermoelectric figure of merit is 0.014. Hence, modifying the optical, electric, thermal and thermoelectric properties of the thin films enables their suitability for applications as transparent electrodes in photovoltaic systems and touch displays, amongst other devices.