Advanced cost effective and sustainable transparent conductors based on titania for large area applications
The general scarcity of raw materials and the enormous cost pressure of industrial production are forcing industry andR&D institutions to develop innovative transparent conductive oxides (TCOs) by using new, improved and sustainable(non-critical) materials. Nb-doped titania (TiO2:Nb) is such a promising novel and nonpolluting TCO material, which shows some benefits for applications. Beside the high refractiveindex of ~ 2.5 (at 550 nm wavelength), TiO2:Nbis resistant under real climate conditions. This opens the ability for applications in the outdoor field, for example in the automotive or architectural area. The results of investigations on TiO2:Nb thin film deposited on large area substrates by sputtering with high deposition rates are reported. As deposition method we used the direct current sputtering of780 mm length substoichiometric oxide tubular target arranged in a rotatable magnetron system in a pilot scale in-line sputtering plant. The films were grown on unheated substrates and then thermally annealed at temperatures of 450°C. The influence of the oxygen partial pressure in the sputtering gas and the annealing in vacuum and hydrogen atmosphere, on the properties of TiO2:Nb were investigated. We observed at a 100 nm TiO2:Nb thin film deposited on Borofloat® substrate after annealing a resistivity of 9.4 x 10-4 Ocm, 82 % transmittance in the visible range and a refractive index of~2.5 for a wavelength of 550 nm. Furthermore we evaluated the changed properties of the films after an outdoor storage of around three hundred days.