High-performance electrochromic devices based on poly[Ni(salen)]-type polymer films.

We report the application of two poly[Ni(salen)]-type electroactive polymer films as new electrochromic materials. The two films, poly[Ni(3-Mesalen)] (poly[1]) and poly[Ni(3-MesaltMe)] (poly[2]), were successfully electrodeposited onto ITO/PET flexible substrates and their voltammetric characterization revealed that poly[1] showed similar redox profiles in LiClO4/CH3CN and LiClO4/ propylene carbonate (PC), while poly[2] showed solvent dependent electrochemical responses. Both films showed poly-electrochromic behaviour, exhibiting yellow, green and russet colours according to their oxidation state, and promising electrochromic properties and higher electrochemical stability in LiClO4/PC supporting electrolyte. In particular, poly[1] exhibited a very good electrochemical stability changing colour between yellow and green (λ = 750 nm) during 9000 redox cycles, with a charge loss of 34.3 %, an optical contrast of ΔT = 26.2 % and an optical density of ΔOD = 0.49, with a colouration efficiency of η = 75.55 cm2 C-1. On the other hand, poly[2] showed good optical contrast for the colour change from green to russet (ΔT = 58.5 %), although with moderate electrochemical stability. Finally, poly[1] was used to fabricate a solid state electrochromic device using lateral configuration with two figures of merit: a simple shape (typology 1) and a butterfly shape (typology 2); typology 1 showed the best performance with optical contrast ΔT = 88.7 % (at λ = 750 nm), colouration efficiency η = 130.4 cm2 C-1 and charge loss of 37.0 % upon 3000 redox cycles.