Plasmonic Oxygen-Deficient TiO2-xNanocrystals for Dual-Band Electrochromic Smart Windows with Efficient Energy Recycling

Abstract

Dual-band electrochromic smart windows capable of the spectrally selective modulation of visible (VIS) light and near-infrared (NIR) can regulate solar light and solar heat transmittance to reduce the building energy consumption. The development of these windows is however limited by the number of available dual-band electrochromic materials. Here, plasmonic oxygen-deficient TiO(2-x)nanocrystals (NCs) are discovered to be an effective single-component dual-band electrochromic material, and that oxygen-vacancy creation is more effective than aliovalent substitutional doping to introduce dual-band properties to TiO2NCs. Oxygen vacancies not only confer good near-infrared (NIR)-selective modulation, but also improve the Li(+)diffusion in the TiO(2-x)host, circumventing the disadvantage of aliovalent substitutional doping with ion diffusion. Consequently optimized TiO2-xNC films are able to modulate the NIR and visible light transmittance independently and effectively in three distinct modes with high optical modulation (95.5% at 633 nm and 90.5% at 1200 nm), fast switching speed, high bistability, and long cycle life. An impressive dual-band electrochromic performance is also demonstrated in prototype devices. The use of TiO2-xNCs enables the assembled windows to recycle a large fraction of energy consumed in the coloration process ("energy recycling") to reduce the energy consumption in a round-trip electrochromic operation.