Electrochromic Performance of Sputtered NbTi-Based Mixed Metal Oxide Thin Films with a Metallic Seed Layer

An attempt has been made to promote the efficiency of the electrochromic (EC) windows to perform at a faster switching rate with good coloration and easy recyclability. In this work, ion-assisted pulsed DC unbalanced confocal magnetron sputtering is used to fabricate mixed metal oxide thin films of Nb and Ti (which are termed as NTO) for EC applications. Further, to increase the EC efficiency of this film, a very thin metallic seed layer is incorporated between the substrate and the film using the layer-by-layer (LBL) coating strategy. The film was prepared by two steps: (i) very thin metallic seed layer coating and (ii) mixed metal oxide NTO layer coating. The metal layer was made of a Nb metal, Ti metal, and NbTi mixed metal, which was coated with the substrate and NTO layer, resulting in three different films, namely, Nb-NTO, Ti-NTO, and NbTi-NTO. The EC properties of these three films were studied in 1 M LiClO₄ dissolved in propylene carbonate and compared with the as-prepared NTO film. The results showed that the Nb-NTO film showed better EC properties, fast switching, better stability, and good recyclability. To check the stability, the film was subjected to prolonged cycling of 500 cycles with a harsh anodic and cathodic sweep at the scan rate of 100 mV s^-1. The UV-Vis spectrum confirmed the Li⁺ trapping in the films after prolonged cycling. To detrap the ions from the host surface, galvanostatic detrapping is carried out called rejuvenation studies. The rejuvenation rate of films is studied at a constant current loading of ∼2 × 10^-5 A cm^-2. To check the commercialization of the EC window, we successfully fabricated the Nb-NTO device with a PEO-LiClO₄-based polymer gel electrolyte.