Divalent Viologen Cation-Based Ionogels Facilitate Reversible Intercalation of Anions in PProDOT-Me₂ for Flexible Electrochromic Displays

The electrochromic (EC) polymer poly (3,4-(2,2-dimethylpropylenedioxy)thiophene) (PProDOT-Me-2) is expected to be used in flexible e-paper displays because of its great optical modulation ability and inherent flexibility. While the EC effect is primarily determined by the anions and cations in the electrolyte, yet suffers from inorganic salt based on monovalent Li+ cations and corresponding anions, such as lithium perchlorate(LiClO4), lithium bis(trifluoromethane sulfonyl) imide (LiTFSI), and lithium trifluoromethane sulfonate (LiTRIF), which may impact the overall EC performance of the EC device caused by insufficient ion doping/de-doping processes. Herein, the divalent viologen cation-based ionogel (VGE) is developed to tackle the challenge. Owing to its more anions design, the doping/de-doping process in the PProDOT-Me-2 is more sufficient, thereby enhancing the optical modulation range (Delta R = 39.4%) of PProDOT-Me-2, compared to monovalent Li+ cation-based ionogel (Delta R = 13.3%). Meanwhile, the VGE has good interface contact with PProDOT-Me-2 and the flexible electrode, which makes the VGE-based EC device (V-ECD) exhibit commendable mechanical stability. To demonstrate the potential application in flexible e-paper displays, the simple eight-digit EC display device is assembled from seven V-ECDs, each of which hasa high switching speed, robust cycling stability, and low operating energy consumption.