Nanostructure-dependent colouration efficiency of electrochromic coatings using 0D, 1D, and 2D WO3 for smart windows

Towards the development of highly efficient electrochromic coatings, the crystallinity, morphology (e.g. size and shape) of electrochromic nanomaterials, and their charge insertion capacities play a significant role. Herein, we report the structure-dependent colouration effciency in electrochromic coatings based on the use of 0D, 1D and 2D tungsten trioxide (WO 3 ) nanostructures. A series of WO 3 with different nanostructures were prepared and used as working electrodes to fabricate electrochromic devices for smart windows applications. Facile spray coating was applied on fluorine-doped tin oxide (FTO) substrate to make ∼70 ​% transparent working electrodes to investigate their charge insertion capacities, electrochromic active surface area, and colouration efficiency. Results showed that the 2D WO 3 nanoflakes displayed the highest diffusion coefficient for the intercalation of 1.52 ​× ​10 −10 ​cm 2 /s with an increased electrochemical active surface area of 25.10 ​mF/cm 2 , a large modulation of optical reflectance (42.63 ​%) with 3.79 ​s shorter response time for bleaching and a greater colouration efficiency (CE) value (89.29 ​cm 2 /C) at 700 ​nm compared to the CE value for 1D WO 3 (of 22 ​cm 2 /C) and 0D WO 3 (8 ​cm 2 /C). The outcome of this study provides a new insight and valuable contribution to design an efficient electrochromic coating by controlling and optimising the nanostructures of selective electrochromic materials.