Colorless-to-black electrochromic materials and solid-state devices with high optical contrast based on cross-linked Poly(4-vinyltriphenylamine)

Abstract

Poly(4-vinyltriphenylamine) (PVTPA) was synthesized, and cross-linked poly(4-vinyltriphenylamine) (PVTPA-CLn) films with a thickness of 260 nm (CL1), 510 nm (CL2), and 680 nm (CL3) were prepared by electropolymerization. Using the PVTPA-CL2 and PVTPA-CL3 films as active materials, the electrochromic devices (ECDs) were fabricated. The structures of the devices were indium tin oxide (ITO) glass/gel electrolyte/PVTPA-CL2/ITO glass (ECD 1) and ITO glass/gel electrolyte/PVTPA-CL3/ITO glass (ECD 2). The electrochromic properties of the PVTPA, PVTPA-CLn films, and ECDs were investigated. Among them, the PVTPA-CL2 and PVTPA-CL3 films exhibited reversible color changes from colorless to gray-green and from colorless to black upon electrochemical doping and dedoping, respectively. The optical contrast of the PVTPA-CL2 and PVTPA-CL3 films were 81.0% and 84.3% at 750 nm, respectively. The ECD 1 could reversibly change between colorless and gray-green under different voltages, and it exhibited 78.3% optical contrast at 750 nm. Notably, ECD 2 could reversibly change between colorless and black under different voltages, and it exhibited 85.0% optical contrast at 750 nm. ECD 1 had shorter switching time than ECD 2, its coloring and bleaching times were 9.5 and 7.3 s, respectively. Both ECD 1 and ECD 2 exhibited reasonable electrochemical cyclic stability.