Optical and electrical performance of transparent conductive TiO₂/Cu/TiO₂ multilayers prepared by magnetron sputtering

TiO₂/Cu/TiO₂ (TCT) multilayers were deposited by dc pulsed magnetron sputtering on glass substrates for the possible use as transparent conducting oxide (TCO). The thicknesses of copper (Cu_d) interlayers were 0, 8, 10, 12, 13 and 15 nm. The changes in structural, optical and electrical properties of the TCT multilayers have been investigated as a function of Cu_d. XRD examination revealed that, all studied TCT multilayers have rutile TiO₂ crystalline structure with different orientations, whereas no peaks have been indexed for the Cu. The refractive index (at 650 nm) of the TCT multilayers decreased from 2.39 to 1.90 and the optical band gap values decreased from 3.77 ± 0.02 to 3.66 ± 0.02 eV as the thickness of the Cu interlayer increased from 8 to 15 nm. It has been found that the electrical resistivity of TCT multilayers decreased from 1.4 × 10⁻⁴ to 3.2 × 10⁻⁵ Ω cm with increasing Cu interlayer thickness from 8 to 15 nm. The TCT film with 10 nm Cu interlayer has a sheet resistance of 13.7 Ω/sq, an average transmittance value of 87.1% (in the wavelength ranging from 500 to 800 nm) and highest figure of merit value of 1.84 × 10⁻² Ω⁻¹. Accordingly it can be considered as superlative TCT film which can be potentially used as transparent conductor electrode for solar cells and other optoelectronic applications.