Sputter-deposited nickel oxide for electrochromic applications

Thin films were produced by sputtering of metallic Ni in Ar/O-2 and Ar/O-2/ H-2 atmospheres. Systematic studies of these films were carried out in elec trochromic devices with tungsten oxide and either proton or lithium conduct ing electrolytes. No major difference was found between devices using nicke l oxide films made in the presence or absence of hydrogen. A practically im portant result is that both kinds of nickel films can be laminated in devic es with tungsten oxide without precycling any of the films in a liquid elec trolyte. Devices with the used Li+ and H+ conducting electrolytes have simi lar properties, suggesting that all of them may be relying on proton transp ort, presumably originating from adsorbed water. From a theoretical point o f view, attention is drawn to the fact that the tap of the NiO valence band consists of Ni 3d electron states, in contrast to the O 2p states at hand for most other electrochromic oxides. The anodic electrochromism of nickel oxide may be explained by assuming that the 3d electrons can be reversibly extracted from and inserted into the film without affecting the metal-oxyge n bonds. (C) 1998 Published by Elsevier Science B.V.. All rights reserved.