Development of Homogenous n-ZnO/TiO₂ Thin Film Dual-Layer Structure Utilizing the Spin-Coating Technique

Titanium dioxide (TiO₂) and zinc oxide (ZnO) thin films have recently garnered attention as promising inorganic semiconductor materials in thin-film photovoltaic applications. Aside from a single layer, a combination of TiO₂ and ZnO layers has been studied since both materials have enormous potential in optical applications. This paper demonstrated deposition of n-ZnO/TiO₂ dual-layer thin films utilizing the sol-gel deposition via spin coating. One of the important steps for n-ZnO/TiO₂ dual-layer thin film to undergo the recrystallization process is the annealing treatment to produce a high-quality thin film. By varying different annealing temperatures, the optimal annealing setting for n-ZnO/TiO₂ dual-layer thin film was 500 °Ⅽ for 2 hours. For structural properties, high intensity with preferred oriented n-(002)ZnO/(101)TiO₂ dual-layer thin film was achieved, showing anatase phase for TiO₂ and hexagonal wurtzite structure for ZnO. A compact, dense, and uniform surface morphology was observed for the n-ZnO/TiO₂ dual-layer thin film. The thickness was 266 nm for TiO₂ and 233 nm for the ZnO layer. The transmittance spectrum has also been achieved up to 70% at a wavelength of 400 nm. After the extrapolated plot, the band gap energy evaluated was 3.15 eV. In summary, the solar cell performance benefited from annealing treatment in refining the characteristics of the thin film.