A charge transfer-induced self-adsorption color-changing device

Electrochromic smart windows (ECWs) have emerged as a promising technology for energy-saving applications in buildings, transportation, and aerospace. However, the reliance on external power sources limits their sustainability and operational flexibility. Although self-coloration/bleaching can be achieved by introducing active metal electrodes, the recovery of ECWs to their initial states typically requires an external power source. Herein, we report a self-adsorption color-changing device (SACD) by combining a Zn anode and a Pt cathode with an electrolyte containing butyl-substituted viologen (BSV-1), where the spontaneous coloration and bleaching of BSV-1 adsorbed on a fluorine-doped tin oxide (FTO) substrate are enabled through interfacial charge transfer driven by the intrinsic potential difference between FTO and Zn and between FTO and Pt, respectively. Without extra power, an ultralow transmittance of 0.2% and a maximum optical modulation of 71.3% at 550 nm can be achieved within 7.5 s. This work pioneers a self-powered electrochromic system consisting of BSV-1 and metal electrodes that enables spontaneous coloration and bleaching control within a sealed device. Energy consumption simulations show that the SACD smart window delivers robust energy savings across climates and strong potential for building energy management. The novel SACD eliminates the applied power dependency of conventional ECWs, and advances the development of eco-friendly smart windows for achieving carbon neutrality goals.