Three Carbazole-Based Polymers as Potential Anodically Coloring Materials for High-Contrast Electrochromic Devices

Three carbazole-based conjugated polymers (poly(3,6-di(2-thienyl)carbazole) (PDTC), poly(2,7-bis(carbazol-9-yl)-9,9-spirobifluorene) (PS2CBP), and poly(3,6-bis(N-carbazole)-N-ethylcarbazole) (PCEC)) are synthesized using electrochemical polymerization. The spectroelectrochemical studies indicate that the PDTC, PS2CBP, and PCEC films show reversible electrochromic behaviors in their redox states, and the PS2CBP film shows a distinct color transition with four various colors (gray at 0 V, grayish-green at 1.0 V, moss green at 1.2 V, and foliage green at 1.4 V). The maximum optical contrast of the PS2CBP and PCEC films is 39.83% at 428 nm and 32.41% at 420 nm, respectively, in an ionic liquid solution. Dual-type electrochromic devices (ECDs) that employ PDTC, PS2CBP, or PCEC film as an anodic layer, and PProDOT-Et(2) film as a cathodic layer, were constructed. The as-prepared PCEC/PProDOT-Et(2) ECD shows high optical contrast (38.25% at 586 nm) and high coloration efficiency (369.85 cm(2) C(−1) at 586 nm), and the PS2CBP/PProDOT-Et(2) ECD shows high optical contrast (34.45% at 590 nm), good optical memory, and good long-term cycling stability.