Effects of Electrolyte Solutions and Their pH on the Electrochromic Cycling Stability of Reactively Sputtered WO3 Thin Fims

Abstract

WO3 thin films were prepared by reactive sputtering and their electrochromic (EC) cycling characteristics were examined in aqueous electrolyte solutions with a pH range from 1 to 6. These solutions contained H2SO4 and a supporting electrolyte of either, K2SO4 or Na2SO4, which was added to maintain a constant ionic conductivity. Stable EC cycling was achieved in solutions containing K2SO4 with pH from 1.5 to 3.6, whereas some degradation occurred in solutions containing Na2SO4. In neutral solutions, the WO3 films peeled off within 20 cycles, regardless pf the type of electrolyte. A maximum transmittance change from 38 to 90%, and stable EC cycling up to 100 cycles were obtained in acidic electrolytes containing H2SO4 + K2SO4 with a pH of 1.5 to 2.5.