Nickel-tungsten oxide thin films: Enhanced switching kinetics via thermal treatment for energy-efficient smart window applications

초록

Nickel tungsten oxide (NT) thin films were fabricated on fluorine-doped tin oxide (FTO) substrates using RF sputtering at varying substrate temperatures, viz., RT, 150 degrees C, 250 degrees C and 350 degrees C and tested as a counter electrode for electrochromic devices (ECDs). Structural investigations demonstrated that tungsten inclusion impaired the crystallinity of the NiO, leading to amorphization under all deposition conditions. Raman and XPS analysis validated the presence of Ni2+ & Ni3+ ions, with Ni vacancies acting as active defect sites for Li+ ion transport. Electrochemical and optical analysis revealed that the substrate temperature greatly influenced the electrochromic performance of the film. Increasing substrate temperatures resulted in higher film density and decreased nickel vacancies, constraining Li+ intercalation channels and hence, reducing electrochromic efficiency. The NT film fabricated at 150 degrees C demonstrated optimal performance, achieving enhanced optical modulation (70 % @ 550 nm), rapid switching cycles (0.7 s for bleaching and 1.4 s for coloring), and improved diffusion coefficients. The research findings emphasize the significance of defect engineering and substrate temperature optimization in attaining high-performance nickel-tungsten oxide-based counter electrodes for energy-efficient smart windows.

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