Transition metal oxide electrochromic materials and displays: a review

Thin films of a number of transition metal oxides, when employed as electrodes in the appropriate electrochemical cells, exhibit electrochromism by a reversible ion-insertion mechanism. Cathodically colouring oxides were covered in the first part of this review1. Oxides which colour anodically by an oxidation process, ie those of Ir, Rh, Ni and Co, are considered here. Special attention is given to iridium oxide as the most studied example and as behaviour model. Significant advances in the understanding and development of electrochromic displays are highlighted. Fabrication and performance of display electrode and complete display cells based on these materials is described and compared, and suggestions put forward regarding the most promising electrochromic material/electrolyte combinations for further study. Emphasis is placed on the method and details of film deposition or growth which determine film stoichiometry (including moisture content) and morphology and in turn strongly influence electrochromic behaviour.