Mixed metal oxides as optically-passive ion storage layers in electrochromic devices based on metallopolymers

Electrochromic devices (ECDs) based on iron metallopolymers (Fe-MEPE) and different oxide-based ion storage electrodes on fluorine-doped tin oxide (FTO)-coated glass as transparent, conductive substrates are investigated in detail. Titanium-manganese oxide (TMO) thin film electrodes deposited by reactive magnetron co-sputtering on FTO glass were compared to commercially available titanium-vanadium oxide (TiVOx) for use as optically-passive ion storage layers. The ECDs with Fe-MEPE combined with TiVOx (coloration efficiency η = 2 cm2 C−1 at 584 nm) and Ti-rich TMO (η = −4 cm2 C−1) are blue-purple in the dark state at 0 V and become highly transmissive when 1.5 V is applied with a visible light transmittance (τv) change from 28% to 69% and 21% to 57% in 3 s and 13 s, respectively. The ECDs show fast responses and high reversibility over more than 100 cycles. The combination of Fe-MEPE and Mn-rich TMO (η = −24 cm2 C−1) leads to a dark brown ECD, which can be brightened at 2.5 V (τv: 4% ↔17%, 9 s for decoloring). •Detailed investigation of ECDs is carried out with Fe-MEPE and optically-passive mixed metal oxide electrodes.•ECDs (Fe-MEPE/TiVOx or Fe-MEPE/TMO) exhibit high optical contrast, coloration efficiencies > 450 cm2 C−1, and fast response.•ECDs are fabricated with high transmittance and color neutrality in the bright state.