Visible Light–Near-Infrared Dual-Band Electrochromic Device

Abstract

We herein propose a proof of concept of a full dual-band electrochromic (EC) device able to selectively modulate solar light between 300 and 1600 nm. Dual-band control was achieved by exploiting the complementarity and cooperation of two earth-abundant and nontoxic transition metal oxide nanocrystalline materials able to absorb two different spectral regions when electrochemically charged. The active materials were obtained through a microwave-based synthetic protocol able to produce massive amounts of ligand-free water-soluble TiO2@WO3–x colloidal heterostructured nanocrystals. The inorganic heterostructures were deposited via a spray-coating airbrushing method. Graphene was adopted as a near-infrared (NIR) transparent material for the realization of conductive substrates. The nano-dimensions and stable solubility of active materials during the deposition process endorse the development of scattering-free nanostructured electrodes and high device transparency under open-circuit conditions, respectively. The spectro-electrochemical properties of the as-made nanostructured electrodes were evaluated in relation to pure WO3–x and TiO2 single nanomaterials and a blend of these. The heterostructured architecture ensures a lower optical haze (around 8% of total radiation) as against the blend, contributing to improving the overall EC performance. The TiO2@WO3–x-based device shows 67% NIR shielding while preserving 60% of visible (VIS) transparency under cool-mode conditions and 89% screening of VIS and NIR radiation under the dark mode. These results represent an important step forward in the development of scalable dual-band EC devices.