Highly flexible electrochromic devices enabled by electroplated nickel grid electrodes and multifunctional hydrogels.

Flexible electronics, as a futuristic technology, is presenting tremendous impact in areas of wearable displaying, energy saving, and adaptive camouflage. In this work, we constructed a simple triple-layered electrochemical device with high flexibility using the electroplated nickel (Ni) grid electrode and the multifunctional hydrogel. The Ni grid electrode with low resistance (0.5 Ω/sq), high optical transparency (84.8%) and good mechanical flexibility, is beneficial for efficient electron injection, while the transparent lithium chloride hydrogel functions simultaneously for ion storage, ion transportation and counter-conducting. The thin polymer poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS) film is utilized as the electrochromic (EC) material and it also distributes the electrons evenly for uniform coloration. The triple-layered EC architecture not only simplifies the manufacturing procedures but also improves the device performance in terms of optical contrast and mechanical robustness. The device shows fast response for coloration and bleaching with an absolute transmittance contrast of 40% and a contrast retention over 72% after 2500 bending cycles. The ability of the flexible electrochromic device for conformable attaching was also investigated without obvious performance degradation. The electroplated Ni grid electrode and the multifunctional hydrogel are advantageous in constructing flexible electrochromic devices in terms of the response time, the working stability and the bending capability, paving a way for next-generation flexible electronics.