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.