Novel electrochromic materials and devices for visible – near-infrared dual-band modulation

Dual-band electrochromic materials will allow for the design of a next generation of solar-control fenestration units providing additional energy savings in terms of lighting, cooling and heating requirements through their unique ability to selectively filter and independently modulate the visible and infrared wavelengths. In order to impart such selective control over these wavelength regions of interest, chosen compositions of metal oxides or doped metal oxides are utilised. In these, reversible electrochemical mechanisms take place, such as capacitive charging as well as faradaic ion insertion coupled to redox reactions. Such electrochemical mechanisms are accompanied by simultaneous optical property changes. This research work focuses firstly on synthesizing “self-doped” version of one of the widely studied electrochromic metal oxide i.e. sub-stoichiometric tungsten oxide (WO3-δ). Superior selective control is promoted in obtaining monoclinic (m-WO3-x) and hexagonal (h-WO3-y) phases accompanied with distinct nanocrystal morphologies, using a refined colloidal synthesis protocol. Furthermore, the influence of each crystal phase on ion-transfer kinetics, and the effect of their distinct morphologies on plasmonic near-infrared light absorption, are discussed. Meanwhile, the capability of dual-band modulation for the novel h-WO3-y phase is demonstrated, along with the existing m-WO3-x phase. Additionally, a novel class of electrochromic materials composed of niobium and tungsten bimetallic oxides (Nb,W)Ox is synthesized via both a facile hydrothermal methodology and an original colloidal synthesis procedure, and the influence of the Nb:W ratio on crystal structure, morphology, electrochemical and electrochromic response are studied. Importantly, two novel formulations of (Nb,W)Ox at Nb:W mol ratios of 0.78 and 1.00 are identified, and highlighted for their efficient dual-band modulation capabilities. Lastly, this work opens perspectives towards developing more optically functional electrochromic devices, towards the fabrication of novel smart windows of increased energy efficiency.