Photo-Patternable Acrylate Viologen Derivatives for Intrinsically Stretchable Multi-Color Electrochromic Devices

Following the development of highly deformable and mechanically robust electronic devices, the reserchers have begun to focus on the creation of stretchable electronics. Stretchable electronics have attracted significant interest for their potential in human-conformable applications, such as wearable devices and biomedical devices. To implement these applications, stretchable devices need to be deformed into various shapes while simultaneously low power consuming, lightweight offering the immense potential to enhance human lives with greater convenience. Among existing candidate devices, Electrochromic displays (ECDs), which is employed for information displays and biological camouflaging skin, is promising as a next-generation wearable display. Compared with other display technologies such as LCDs and QD displays, ECDs offer several notable advantages, including a simple structure, high contrast, the absence of backlighting, and low driving voltage operation. ECDs utilise electrochromic (EC) materials to achieve low voltage-controllable reversible colour changes by modification of optical properties, thereby providing the advantage of a simplified device structure. For example, WO3-based inorganic ECDs, a well-known inorganic EC material, have demonstrated exceptional cyclic stability and rapid switching capabilities, making them highly effective in various applications. However, due to its brittle characteristic, the material presents challenges in the fabrication of deformable displays. To overcome this limitation, the deposition of WO3 on silver nanowires (AgNWs) has been investigated, enabling the WO3 to endure mechanical stress similarly to the AgNWs. Nevertheless, after the deposition of WO3, further deposition of other materials on the same surface becomes extremely difficult, significantly limiting the creation of multi-color displays. Due to these issues, other approaches have made use of deformable organic EC materials, employing organic and polymeric materials with elastomers to construct inherently stretchable active matrix displays. Additionally, EC materials is limited to pixelation and their integration into deformable devices. These issues are primarily attributed to non- patternable, which limited the implementation of stretchable display. In this study, we demonstrate a material design and facile device fabrication method for developing photo-patternable, stretchable, and multi-colour electrochromic devices using acrylate-substituted viologens. By integrating acrylate-substituted viologens into EC gels, we demonstrated intrinsically stretchable and photo-patternable EC devices (R, G, B) with pixel resolutions below 50 µm, composed of acrylate-substituted viologens homogeneously mixed with anodic material, ionic liquid, and a photo-curable elastomeric matrix. The three ECDs, which correspond to deep red, green, and blue, exhibited stable characteristics during 12,000 seconds of repetitive operation without any degradation in device performance. The pixelation process is induced directly on an elastomeric substrate using UV light, allowing for the implementation of multi-color stretchable ECDs. Additionally, we have successfully addressed a significant issue regarding intimate contacts between electrodes and pixels which often lead to degraded coloration and mechanical failures such as electrode delamination and fatigued cracks. This was achieved by filling the air gap with ion gel and incorporating a pixel define layer (PDL). When Ion gel spacer fills the air gap in devices, the ion gel spacer serves not only to provide an electrical path and bind all the interconnected layers but also to evenly distribute surface area stress across the entire device. As a result, the fully colored stretchable electrochromic device exhibited significant durability, retaining promising color characteristics following 1,500 cycles of mechanical strain testing at strains below 30%.