Modification of the electrochromic response of WO₃ thin films by oxygen backfilling

The effect of oxygen backfilling on WO₃ electrochromic thin films has been studied. Previously it was shown that O₂ backfilling reduced the corrosion rate in H₂SO₄. In this phase of the study it has been shown that O₂ backfilling also affects the EC response. For example, the coloration speed and optical efficiency were decreased while bleaching speed and self‐erasure rate were increased. The current injection during coloration was found to be controlled by the same mechanism as the films without backfilling (i.e., WO₃ resistivity and Helmholtz double layer). However, the magnitude of the current passed was lowered due to increased film resistivity from backfilling. The optical absorption maximum remained unchanged while the thermal hopping energy increased with oxygen backfilling. These observations suggest that a decreased density of optically active absorption centers resulted in the lower optical efficiency.