Investigation of Varying Particle Sizes of Dry-Deposited WO3 Particles in Relation to Performance of Electrochromic Cell

Electrochromic cells were fabricated via a nanoparticle deposition system (NPDS) using different particle sizes of monoclinic tungsten oxide (WO3). Mixtures of micro-and nano-sized WO3 powders in the ratios of WO3 (micro):WO3 (nano) = 9 : 1, 5 : 5 and 1 : 9 vol%, were used in this study. NPDS, which was used to fabricate the electrochromic layer, is a low-cost process that can cover a large deposition area and provides a highly porous film. This method can replace sol-gel and sputtering methods, which are expensive and have environmental issues. The WO3 electrochromic layers displayed different surface structures that could adsorb Li+ ions. The transmittance change, cyclic switching speed and coloration efficiency (CE) results demonstrated that the electrochromic cell made with the mixed WO3 (micro):WO3 (nano) powders had better performance than that of the electrochromic cell made with separate micro-sized single powders. Various analyses showed that the WO3 mixed powders contained larger sites for Li+ ion adsorption compared with the single-sized powder because of a structure consisting of a compact layer of micro-WO3 with a porous layer of nano-WO3. Consequently, a cell composed of mixed-particle electrochromic layer showed higher transmittance change, CE and electrochromic performance than a cell made with a micro-sized single powder.The work was supported by the Energy Efficiency of Resources Core Technology Program (No. 20142020103730) and Human Resources Development Program (No. 20174030201830) of the Korean Institute of Energy Technology Evaluation and Planning (KETEP), granted financial resources from the Ministry of Trade, Industry and Energy, Republic of Korea and a grant from the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (No. NPF-2015R1A2A1A13027910)