Metallopolymers and non-stoichiometric nickel oxide: Towards neutral tint large-area electrochromic devices

Wet-chemical approaches were utilized to fabricate electrochromic (EC) thin films of different chemical nature, but compatible to each other in terms of coloration and electrochemical properties. A metallo-supramolecular polyelectrolyte (Fe-MEPE) thin film is shown to exhibit a large visible light transmittance change (Dtv) of 54% when switched from deep blue-violet (Fe2+) to colorless (Fe3+). On the other hand, a soft sol-gel peroxo-based approach was pursued to fabricate non-stoichiometric nickel oxide (Ni1-xO) thin films on transparent conductive glass at low process temperature. Ni1-xO, due to the Ni2+/Ni3+ redox couple, shows an EC response with a Dtv of 44% when switched from a colorless state (Ni2+) to a grey-brown mixed-valence state (Ni2+/Ni3+). Proof-of-concept is provided for a glass-based EC device combining Fe-MEPE and Ni1-xO electrodes. The excellent EC performance is manifested in a Dtv of 28% for the full cell and a low haze of <2%. The EC films presented can be deposited on transparent conductive substrates via spin-coating, dip-coating, or slot-die deposition. The viability of this approach for later industrial production is demonstrated by the example of roll-to-roll (R2R) processing on transparent conductive films (TCF).