Development of self-powered multicolored smart windows utilizing viologen derivatives†

In recent years, smart windows that provide energy-efficient solutions for the construction and transportation sectors have attracted considerable interest as a result of increasingly severe environmental issues. Electrochromic windows have emerged as a prominent option because of their high coloring efficiency and broad optical modulation range. However, traditional electrochromic devices necessitate the use of an external electric field to operate, which not only increases energy consumption but also poses safety risks. In this study, we propose a novel self-powered electrochromic smart window that utilizes the principles of self-charging batteries to achieve optical modulation across a wide spectrum of visible light. This device utilizes viologen derivatives as electrochromic materials due to their highly reversible redox reactions and the ease with which their colors can be manipulated. The devices can exhibit three distinct display states, transitioning from colorless or pale yellow to blue, purple, and green, by varying the types of viologen derivative electrochromic materials employed. Notably, simply disconnecting the zinc anode from the conductive glass cathode enables the self-recovery of the electrochromic state, thereby restoring the initial transmittance level. This recovery takes place as the viologen cation radical spontaneously oxidizes to form the divalent ion; a process facilitated by oxygen dissolved within the gel electrolyte. The device not only features a multicolor display and efficient optical modulation but also demonstrates excellent cycle stability and safety. Consequently, the smart window presented functions as a multifunctional device, serving both as an electrochromic window and an energy storage unit. This innovative self-powered multicolor display device significantly broadens the application scope of electrochromic smart windows. It achieves not only the shading effect of optical modulation but also meets the energy-saving and flexible design needs in the fields of architecture and transportation, thereby providing opportunities for further applications in the new energy industry.