Facile Solution Synthesis of Tungsten Trioxide Doped with Nanocrystalline Molybdenum Trioxide for Electrochromic Devices

A facile, highly efficient approach to obtain molybdenum trioxide (MoO₃)-doped tungsten trioxide (WO₃) is reported. An annealing process was used to transform ammonium tetrathiotungstate [(NH₄)₂WS₄] to WO₃ in the presence of oxygen. Ammonium tetrathiomolybdate [(NH₄)₂MoS₄] was used as a dopant to improve the film for use in an electrochromic (EC) cell. (NH₄)₂MoS₄ at different concentrations (10, 20, 30, and 40 mM) was added to the (NH₄)₂WS₄ precursor by sonication and the samples were annealed at 500 °C in air. Raman, X-ray diffraction, and X-ray photoelectron spectroscopy measurements confirmed that the (NH₄)₂WS₄ precursor decomposed to WO₃ and the (NH₄)₂MoS₄-(NH₄)₂WS₄ precursor was transformed to MoO₃-doped WO₃ after annealing at 500 °C. It is shown that the MoO₃-doped WO₃ film is more uniform and porous than pure WO₃, confirming the doping quality and the privileges of the proposed method. The optimal MoO₃-doped WO₃ used as an EC layer exhibited a high coloration efficiency of 128.1 cm²/C, which is larger than that of pure WO₃ (74.5 cm²/C). Therefore, MoO₃-doped WO₃ synthesized by the reported method is a promising candidate for high-efficiency and low-cost smart windows.