High contrast hybrid electrochromic film based on cross-linked phosphonated triarylamine on mesoporous antimony doped tin oxide

Abstract

A novel electrochromic material consisting of a phosphonate-substituted triarylamine (TAA-P) precursor on mesoporous antimony doped tin oxide (ATO) was prepared. When subjected to anodic potential, surface-confined TAA-P undergoes in situ dimerization as demonstrated by electrochemical and spectroscopic methods. The newly formed dimer tetra-N-phenyl benzidine (TPB) exhibits multi-electrochromic behavior, from colorless TPB0 via the bronze colored radical TPB+•, and further to green TPB2+ species. The films show a remarkably fast electrochromic response (2.6 s for coloring and 0.3 s for bleaching), high coloration efficiency (−280 cm2/C), and high electrochromic contrast (ΔT = 82% at 700 nm) when switched between colorless and dark green states. The comparison of TPB@ATO with an analogues titanium dioxide hybrid film (TPB@TiO2) revealed the importance of electronic conductivity within the inorganic semiconductor scaffold present in ATO but missing in TiO2 at positive potentials. We have prepared an electrochromic film with the ability to switch from colorless to dark green within a very short time, paving the path for state-of-the-art applications such as optical shutters.