Effect of particle size and amorphous phase on the electrochromic properties of kinetically deposited WO₃ films

다국어 초록 (Multilingual Abstract)

<P><B>Abstract</B></P> <P>The electrochromic (EC) performance of a WO<SUB>3</SUB> film fabricated using a kinetic spray technique (nanoparticle deposition system, NPDS) was examined as a function of the particle size and phase of the WO<SUB>3</SUB> particles. The total transmittance change of the deposited WO<SUB>3</SUB> film containing crystalline nano-sized WO<SUB>3</SUB> particles was 56% at 800nm, which resulted in a large shift in its transmission spectrum after coloring. Moreover, the charge density of the EC film using crystalline nano-sized WO<SUB>3</SUB> particles was 22.06mCcm<SUP>−2</SUP>, which was 2.8 times higher than that of the film composed of crystalline micro-sized WO<SUB>3</SUB> particles (7.97mCcm<SUP>−2</SUP>). Using crystalline nano-sized WO<SUB>3</SUB> particles greatly increased the surface area, increased the number of absorption sites for Li ions inside the film, and thereby improved the charge density and transmittance. The transmittance change of the EC films using dual-phased nano-sized WO<SUB>3</SUB> particles was 64% (at 800nm), which was still higher than that with crystalline nano-sized WO<SUB>3</SUB> particles. The amorphous phase in the dual-phase nano-sized WO<SUB>3</SUB> film provided good diffusion of Li ions; it had a high diffusion coefficient of 1.53 × 10<SUP>−12</SUP> cm<SUP>2</SUP> s<SUP>−1</SUP> that derived from its loosely packed atomic structure. The amorphous region in a heterostructured WO<SUB>3</SUB> film was effective for the fast diffusion of Li ions, while the crystalline nano-sized region in such a film provided a large surface area for an increased number of absorption sites for Li ions. This resulted in a dramatic improvement of the EC performance.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Different size and phase of WO<SUB>3</SUB> particles were deposited using kinetic spray technique. </LI> <LI> Varying size and phase of the WO<SUB>3</SUB> particles, change charge density. </LI> <LI> Nano WO<SUB>3</SUB> provided more absorption sites for Li ions, which improved EC performance. </LI> <LI> Amorphous/crystalline heterostructured WO<SUB>3</SUB> resulted in loosely packed atomic structure. </LI> <LI> Amorphous/crystalline heterostructured WO<SUB>3</SUB> showed the best EC performance. </LI> </UL> </P>