WO3 quantum-dots electrochromism

In the past decades, as an alternative to traditional sputtering deposition process, atmospheric pressure solution-based deposition (APSD), considered as a cost-effective method for the construction of nanostructured electrochromic (EC) films with improved EC performance, is widely studied. However, the inadequate EC performance of the films, especially the poor cycle stability, impedes the development of solution-processed EC films. This paper reports excellent EC performance results for WO3 quantum-dots films prepared by a common APSD process with either Li+ or Al3+ electrolyte: a large optical contrast (97.8% and 94.1% at 633 nm), a fast switching speed (4.5 s and 13.5 s for coloring, 4 s and 10 s for bleaching) and an ultralong cycle life (10000 cycles with 10% optical contrast loss and 20000 cycles without degeneration at 633 nm). The excellent EC performance can be attributed to the ultrasmall size in all three-dimensions and no organic overlayer of WO3 quantum dots, which would greatly shorten the diffusion paths of intercalation ions, decrease interface barrier, provide fast charge-transport and electron-transfer kinetics and high reaction rates. Trivalent Al3+, as an alternative to common monovalent insertion ions (H+, Li+, Na+), was proven to be as an effective insertion ion for WO3 quantum dots. Compared with Li+ electrolyte, the films possess longer cycle life in Al3+ electrolyte, which can be attributed to the smaller ionic radius and the ability to support multi-electron redox reactions of Al3+. This research is an important first step for the fabrication of inexpensive EC smart windows, and should shape the future research on solution-based processes.