Advances in electrochromic device technology: Multiple roads towards superior durability

Most electrochromic (EC) devices must have a service lifetime of many years, and this is particularly so for “smart windows” in buildings with good energy efficiency and indoor comfort. The central part of oxide-based EC devices contains thin films based on W oxide and Ni oxide together with an interposed electrolyte. Depending on operating conditions, these films may show degradation at a slower or faster pace, and means to prevent or reverse this phenomenon, or as a minimum allow reliable lifetime prediction, have been sought ever since the beginnings of EC technology. Here we survey recent endeavors related to EC films of W oxide and Ni oxide and show that (i) electrochemical pretreatment of films in a liquid electrolyte can significantly improve durability, (ii) electrochemical posttreatment in a liquid electrolyte can rejuvenate degraded films, (iii) mixed oxides can have better durability and optical performance than corresponding pure oxides, and (iv) lifetime prediction is possible.