Electrochromic (EC) smart windows, which have the ability to absorb near-infrared (NIR) irradiance, are considered a promising candidate for window technology in sustainable buildings. A step ahead, self-powered electrochromic smart windows not only help modulate indoor ambience but also serve as charge storage devices, thereby enabling off-grid applications. In this context, metallo-supramolecular polymers, a fourth-generation electrochromic material (ECM), offer an added advantage due to their tunable properties and ease of processability, which is facilitated by their solubility in low-boiling solvents. Here, we report a Co(II)-based metallo-supramolecular polymer that provides a facile route for device fabrication, enabling self-powered electrochromism and simultaneously serving as a self-charging zinc-based energy storage device. The dual-functional device exhibits a color change from yellow to blackish, achieving the highest optical modulation with a transmittance change (ΔT%) of 33% between the yellow and blackish states at 700 nm. Again, the blackish state of the device can reduce 37% of solar irradiation and maintain an indoor temperature difference of 9 °C after the irradiation of continuous IR light for 15 min, compared to the transparent yellow shade when used as a smart window. The fabricated ITO/Co-TPYTZ//Zn/ITO electrochromic device (EDC) exhibits a rapid and spontaneous color change from yellow to blackish upon connecting the Zn electrode to the Co-TPYTZ layer, demonstrating self-powered smart window behavior without the need for external voltage. Additionally, the assembled device exhibits a high specific capacitance of 36.4 mAh/g at a current density of 0.5 A/g, providing a visual correlation between the energy storage status and the color of the EC layer. Importantly, the fast (within 6 min) self-charging, as well as the reversible color change behavior of the built-in ECD from blackish to yellow through simple areal oxidation of the blackish Co(I)-TPYTZ layer to the pristine yellow Co(II)-TPYTZ layer, is established. The simplified fabrication process reduces the number of processing steps, thereby enhancing reproducibility and scalability. This work presents a practical approach for developing high-performance and rapidly self-recharging EC smart windows.
Biswas et al. (Thu,) studied this question.