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 electro-chromic (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.