Mixed Molybdenum–Tungsten Oxide as Dual-Band, VIS–NIR Selective Electrochromic Material

The energy efficiency of smart windows can be greatly improved by integrating dual-band electrochromic materials based on nanostructured doped metal oxides, as these allow for the dynamic and independent control of light and heat supplies in buildings, respectively, related to transmitted visible (VIS) and near-infrared (NIR) solar radiations. Mixed molybdenum–tungsten oxides Mo_yW_1−yO_3−δ “MoWOx” are considered as innovative compounds in this context: in comparison with parent WO_3−δ formulations, a remarkable increase of unpaired electrons can be obtained from the formation of a larger amount of both reduced species and oxygen vacancies during the synthetic process of MoWOx materials, with a consequently boosted intensity of light absorption by 850–900 nm wavelengths. Consecutively, spin-coated films obtained from MoWOx structures, solvothermally synthesized for 1 h from 2/1 Mo/W atomic ratios, are shown to be electrochromically commutable through a noticeable VIS-darkened and NIR-transparent warm state, while WO_3−δ benchmarks classically evolve between bright (VIS- and NIR-bleached), cool (VIS-bleached, NIR-opaque), and dark (VIS- and NIR-opaque) states. All in all, such advanced optical functionalities are of high interest for fine-tuning the selectivity and improving the efficiency of electrochromic fenestration solutions, further improving their capacity to adapt to different climates, seasons, and user preferences.