Electrochromic and optical studies on Nb2O5–NiO mixed oxide films for smart window applications

Coatings of Nickel oxide (NiO), Niobium oxide (Nb2O5) and their mixed oxide (Nb2O5–NiO) were deposited on glass and conducting glass substrates by simple spin coating technique. Structural, morphological, optical and electrochemical properties of the mixed oxide (Nb2O5–NiO) films were analyzed and the data was compared with individual oxide coatings. As-prepared Nb2O5–NiO coatings showed transparent in nature, while Li + intercalated Nb2O5–NiO (termed as Li–Nb2O5–NiO) coatings were black in color. In addition, Nb2O5–NiO coatings showed better electrochromic reversibility and fast switching. All the as-prepared and Li+ intercalated coatings were subjected to IR absorption studies. Interestingly, Li–Nb2O5–NiO coatings showed better Infra-red (IR) absorption whereas bleached Nb2O5–NiO coatings did not show any remarkable IR absorption. The Li–Nb2O5–NiO coating absorbed about 65% of IR radiation falling on it and allowed the remaining 35% radiation to pass through the coating. In order to prevent the remaining 35% of IR radiation from passing through the coating, laser treatment was carried out on the coating using Pulsed Laser Deposition (PLD) unit. This laser treated Li–Nb2O5–NiO coatings showed better IR reflectance compared to normal Li–Nb2O5–NiO due to its improved surface roughness. It is concluded that the collective effect of IR absorption (by modifying the electronic structure of materials by ion intercalation) and IR reflectance (by increasing the surface roughness) played on a laser treated Li– Nb2O5–NiO coating resulted in a better IR blocking window.