Electrochromic Coloration of Sputtered Nickel Oxide Films by Injection of Anions (Br- Ions)

Abstract
Electrochromic (EC) coloration of nickel oxide films has been achieved by the injection of anions (Br- ions). This was effected by the use of a polymeric anion conductor. Nickel oxide films were prepared by rf-sputtering in an Ar/O2/H2 atmosphere from a compressed-powder NiO target. In order to achieve reversible EC phenomena, as-deposited films required an aging process (i.e. several cycles of injection and extraction of charge carriers). After aging, charges (Br- ions) were observed to remain in the films. The residual charge in the films was observed to increase with hydrogen content in the sputtering atmosphere, however, coloring efficiency was observed to decrease. It was proposed that the residual charge (Br- ions) was responsible for deactivation of the EC color centers.