Sheet resistance dependence of fluorine-doped tin oxide films for high-performance electrochromic devices

In the present study, we fabricated fluorine-doped tin oxide (FTO) films with different sheet resistances (~10 Ω/□, ~6 Ω/□, and ~3 Ω/□) prepared through the adjustment of deposition time during the horizontal ultrasonic spray pyrolysis deposition (HUSPD) and investigated the effect of electrochromic (EC) performances with different sheet resistances of the FTO films used as transparent conducting electrodes. The results demonstrated that, owing to the increased electrochemical activity, the decrease of sheet resistance accelerated switching speeds of the EC devices. However, for the coloration efficiency (CE), the FTO films with the optimum sheet resistance of ~6 Ω/□ exhibited the highest value as compared to the other samples. The improvement of the CE value can be mainly attributed to high transmittance modulation by the uniform surface morphology of the FTO films to reduce interfacial light-scattering between the WO3 films and FTO films. Therefore, our results provide a valuable insight into the improvement of the performance of the EC devices using the optimum sheet resistance (~6 Ω/□) of the FTO films.