Dual-Band Electrochromic Devices with a Transparent Conductive Capacitive Charge-Balancing Anode

Dual-band electrochromic devices (DBEDs), which can selectively modulate near-infrared (NIR) and visible (VIS) light transmittance through electrochromism, have gained increasing interest as a building energy saving technology. The technology is strongly dependent on the progress in electrochromic materials. Most current research has focused on the dual-band properties of the cathode materials, leaving the charge-balancing anode materials under-explored by comparison. This is a report of our study on the suitability of tin-doped indium oxide (ITO) nanocrystals (NCs) as a capacitive anode material for DBEDs. The ITO NCs are electrically conductive and VIS light transparent throughout the device operating range. As a result, they would not affect the NIR-selective modulation of the electrochromic device like most other anode materials do. The high surface area and good conductivity of the ITO NCs facilitate the adsorption/desorption of anions; thereby increasing their effectiveness as an ion storage thin film on the anode to balance the cathode charge. The best DBED prototype assembled from an ITO NC anode and a WO_3- cathode showed effective and independent control of VIS light and NIR transmittance with high optical modulation (71.1% at 633 nm, 58.1% at 1200 nm), high coloration efficiency (95 cm² C^-1 at 633 nm, 220 cm² C^-1 at 1200 nm), fast switching speed, good bistability, and cycle stability.