Electrochromic behavior of Ni_(1-x)O thin films in various electrolytes

摘要

The present study is focused on alternative electrolytes for electrochromic devices using ionic liquids made of different types of cations as well as free of small cations. In particular, we report the electrochromic behavior of non-stoichiometric nickel oxide thin films grown by reactive RF magnetron sputtering at room temperature in various oxygen partial pressures, namely 2% and 10% P(O_2/Ar+O_2). Whatever the electrolyte composition, upon oxidation, the reversible optical properties from transparent to brownish remains, associated however with different electrochemical responses. In addition, the influence of the conditions of deposition (i.e oxygen partial pressure) on the room temperature deposited thin films morphology, stoichiometry and crystallinity is discussed in relationship with their electrochromic behavior. Higher oxygen partial pressure leads to Ni_(1-x)O thin films showing higher density as well as larger Ni~(3+) content. Cycling in a wide range of ionic liquids electrolytes demonstrates similar optical transmittance modulation of 25% while various mechanisms from insertion to surface phenomena take place.