Electrochromic characterizations of copolymers based on 4,4′-bis(N-carbazolyl)-1,1′-biphenyl and indole-6-carboxylic acid and their applications in electrochromic devices

Abstract

Two homopolymers (poly(4,4′-bis(N-carbazolyl)-1,1′-biphenyl) (PBCz) and poly(indole-6-carboxylic acid) (PInc)) and three copolymers (P(BCz1-co-Inc1), P(BCz1-co-Inc2), and P(BCz1-co-Inc4)) with various BCz/Inc feed molar ratios are electrochemical polymerized on indium tin oxide (ITO) electrode. Spectroelectrochemical properties of polymer films reveal that P(BCz1-co-Inc2) film is yellow in the reduced state, yellowish brown in the intermediate state, and greyish black in highly oxidized states, and it can be reversibly oxidized and reduced with obvious color changes. Five dual-type electrochromic devices (ECDs) are fabricated using the BCz- and Inc-based polymers as coloring layers, and poly(3,4-(2,2-diethylpropylenedioxy)thiophene) (PProDOT-Et2) as the complementary layer. The ECD fabricated using an anodic copolymer P(BCz1-co-Inc2) with a BCz/Inc feed molar ratio of 1/2 has the highest optical contrast (42.0%) and coloration efficiency (634cm2/C) at 587nm. In addition, this ECD has satisfactory optical memory effect and long-term cycling stability.