Colorless-to-black electrochromic devices based on ambipolar electrochromic system consisting of cross-linked poly(4-vinyltriphenylamine) and tungsten trioxide with high optical contrast in visible and near-infrared regions

Electrochromic materials are getting huge attention of recent research owing to their vast applications in the optoelectronic research field. Herein, poly(4-vinyltriphenylamine) (PVTPA) was chemically synthesized. The cross-linked poly(4-vinyltriphenylamine) (PVTPA-CL) film with a thickness of ~480 nm was prepared by electropolymerization process. The color complementary ambipolar electrochromic devices (ECDs) were fabricated using the PVTPA-CL films and ethyl viologen (EV) or tungsten trioxide (WO3) as electrochromic active materials. The structures of ECDs were indium tin oxide (ITO) glass/PVTPA-CL film/GE-1 (PMMA:LiClO4:ACN:PC:EV = 7:3:30:60:3.5, w/w)/ITO glass (ECD 3), ITO glass/PVTPA-CL film/GE-2 (PMMA:ACN:PC:EV = 7:30:60:3.5, w/w)/ITO glass (ECD 4), and ITO glass/PVTPA-CL film/GE-3 ((PMMA:LiClO4:ACN:PC = 7:3:30:60, w/w)/WO3/ITO glass (ECD 5). The electrochromic properties of ECDs were investigated. All the ECDs exhibited reversible color changes between colorless and black under different voltages. Furthermore, ECDs also exhibited high optical contrast in visible and near-infrared region; the optical contrast of ECD 3, ECD 4, and ECD 5 are greater than 62.9%, 61.2%, and 70.6% in the 430–800 nm range, respectively. Compared with ECD 3 and ECD 4, ECD 5 exhibited higher optical contrast in the near-infrared region and shorter switching time, and its coloring and bleaching times were 4.6 s and 3.0 s, respectively. Ambipolar color-complementary colorless-to-black electrochromic device (ECD 5) based on PVTPA-CL and WO3 films is promising for electrochromic smart windows.