Polythiophene -viologen bilayer for electro-trichromic device

Abstract

An electrochromic device, capable of three-level color switching, has been envisaged by exploiting different color switching properties of Ethyl viologen (EV) and Poly (3-hexylthiophene) (P3HT) to make them switch in congruence with each other. The device, consisting of an EV/P3HT bilayer in poly-ethylene oxide matrix, appears magenta, blue or transparent under an appropriate bias. The unbiased device shows magenta colored appearance and turns transparent at a bias of 1 V when P3HT layer is used as anode. The device turns blue on increasing the bias to 1.4 V without changing the polarity. The mechanism of multilevel switching has been identified using UV–Vis and Raman spectroscopic investigations which reveal that the 1 V bias converts the P3HT into polarons and 1.4 V converts the EV dications (EV2+) into free radical. The electrochromic device demonstrates better color contrast (~ 50%) in both the optical domains. The fabricated device shows better switching speeds of ~ 1.5 s and good stability and coloration efficiency along with three-level color switching. However the reported device uses ITO coated glass as substrate, it can be used for all-organic flexible electrochromic device. © 2018 Elsevier B.V.