Rollable and transparent subpixelated electrochromic displays using deformable nanowire electrodes with improved electrochemical and mechanical stability

Abstract

Electrochromic displays (ECDs) have advantages that are required for next-generation wearable devices, but they are limited in terms of electrochromic (EC) material pixelation and application in deformable electrodes. Therefore, in this study, rollable and transparent subpixelated-ECDs with deformable single-walled carbon nanotube (SWCNT)/Pd-coated Ag nanowire (PCSN) bilayer electrodes were developed and successfully confirmed to achieve high electrochemical and mechanical stability. Chemically enhanced PCSN with the Pd thickness controlled to 5 nm was synthesized, and the SWCNTs were deposited to a thickness of 50 nm as bilayers on PCSNs for further chemical and mechanical improvement. To implement deformable displays, the electrode materials and emitting layers must be deformable. The EC gels were elastically deformed even under the condition of an applied external strain of 70%, and to have a Poisson’s ratio of ~0.43. The viologen-based EC gels were used to realize various colors (magenta, blue, and green), and characteristics of the ECDs such as the response time, coloration efficiency, and repeatability were excellent. The redox stability of the rollable ECDs using bilayer electrodes exhibit >100-fold improvement in the redox stability compared with devices with pristine-Ag NWs. The subpixelated-rollable ECDs were simultaneously implemented with subpixels of three colors and were stable in repeated rollable tests for 500 cycles at a curvature radius of 2.5 mm. Consequently, these results indicate that EC materials can be applied to wearable devices, while retaining the advantages of ECDs, by solving the problems related to pixelation and electrodes.