Development of a novel WO3 self-powered electrochromic window technology with a self-rechargeable battery application (ChromoVolt)

Abstract

For zero-energy buildings, electrochromic smart windows are one of the most essential components, but the external power demand makes this purpose ambiguous. Here, we report a self-powered electrochromic smart window (ECSW) operated by internal electrochemical voltage (chromoVolt). This WO3-based ECSW provides a unique structured device as the 2 mm width Al strip (counter electrode) is placed at one side, making the total window transparent from the front or back point. The WO3 working electrode was fabricated by the large-scale roll-to-roll (R2R) slot-die wet coating method. This device goes into coloured (blue) or bleached (transparent) states spontaneously simply by connecting and disconnecting WO3 and Al electrodes respectively. Going into a deep blue stable-colored state takes approximately 2 min and shows a maximum 56.5 % transmittance change at 600 nm wavelength. Also, this ECSW can provide output potential through internal chemical reactions in a transparent state and can be charged up through disconnection: a self-rechargeable transparent battery application. Three small cells of an active area of 30 mm × 15 mm each provide an output voltage of around 3 V and can power up a small white LED light for up to 1 h. All these phenomena make this electrochromic smart window perfect for a zero-energy building.