Electro-optical Performance of All Solid State Electrochromic Devices with NaF Electrolytes

• The NaF film is prepared by e-beam evaporation. • The structure, morphology and optical properties of NaF films are characterized. • The ECDs with the structure of ITO glass/WO 3 /NaF/NiO/ITO are assembled. • The ΔT of the ECD at wavelength of 660 nm is approximately 36.3%. • The t c and t b are 18.2 s and 10.8 s, respectively. Among various energy efficient technologies, electrochromic device can improve energy efficiency via controlling the transmittance of solar energy. However, the high costs, scarce resources on earth, toxicity of Li + based electrolytes still block the commercialization of electrochromic devices. Enlightened by the previous extensively investigated Na + based electrochemical systems, we attempt to study the application of Na + based solid state electrolytes in all solid state electrochromic devices in this study. The structural, morphological and optical performance of NaF films are characterized. The electrochromic devices show fast response (10.6 s for bleaching and 18.2 s for coloring) and high coloration efficiency (112.1 cm 2 C -1 ). This study presents a significant advance in solid state electrolytes and provides new avenues for high-performance electrochromic devices.