Two-step fabrication of Na_xWO₃ thin film via oxygen-vacancy-induced effect for energy efficient applications

Developing solar modulation materials such as alkali tungsten bronzes with high-performance and low-cost fabrication is extremely important for energy-saving project applications in our modern lives. In this paper, sodium tungsten bronze (Na_xWO₃) film was fabricated by a novel approach using a two-step method. Amorphous sub-stoichiometric WO_3-x (0 < x < 1) film was deposited on glass using magnetron sputtering and then formed Na_xWO₃ after post-annealing treatment. Oxygen vacancies and tunnels existing in WO_3-x receive ions such as Na⁺, O^2-, etc. that diffuse from the glass substrate. The Na⁺ ion enters tunnels among WO₆ octahedra. The O^2- ion combines with an oxygen vacancy. The Na_xWO₃ film exhibits excellent infrared shielding performance with less than 10% infrared transmittance and high transmittance for visible light, as well as completely blocking UV light. Compared with traditional wet chemistry methods, this approach is much more concise with low cost, thus having huge potential applications for energy-saving projects.