External Magnetic Field: Enhancing Electrochromic Efficiency of Magnetic Metals Composited WO3 Films Prepared by Sparking Method

This study investigated the impact of magnetic metals (Fe, Ni, and Co) composited WO3 films on the enhancement of electrochromic (EC) performance. These films were fabricated using a one-step sparking method with and without the presence of external magnetic fields (B). The FE-SEM images show that the fluffy morphology (without B) gradually shifts to form a denser surface (with B). This shift is most likely ascribed to the rearrangement of the deposited particles under the magnetic field, leading to an improvement in film reversibility. The Co/W nanocomposite films, among the tested films, exhibited the most significant enhancement, as demonstrated by their reversibility, which increased from 14.4 % (without B) to 73.3 % (with B), and coloration efficiency, which improved from 27.1 cm2/C (without B) to 131.3 cm2/C (with B). These improvements are crucial in the practical application of these materials. Moreover, a minimum resistivity of 0.45 x 10-3 omega cm and a maximum mobility of 183.12 cm2/Vs were observed in this sample. Subsequently, the cobalt-composited tungsten oxide (CoW) films were deeply investigated in term of their morphological, structural, optical, and electrochromic properties under the influence of various magnetic fields at 0-500 mT, labeled as CoW without B, CoW-200, CoW-300, CoW-400, and CoW-500, respectively. Raman spectroscopy confirmed that the Co3O4 crystalline structure in the CoW-300 sample underwent transformation into a robust WO3 monoclinic phase in the CoW-400 sample. In addition, the oS analysis of the CoW-400 sample revealed an oxygen vacancy peak, which facilitated electron transport and improved the conductivity. Finally, an excellent 176.0 cm2/C coloration efficiency and 87.2 % reversibility was obtained for the Co/W composite film prepared by the sparking method under a magnetic field of 400 mT, which is a potential material for electrochromic devices.