Influence of LiPON thickness on the electro-optical performance of inorganic all-solid-state electrochromic devices

Amorphous lithium phosphorus oxynitride (LiPON) films of various thicknesses were prepared by radio frequency (RF) magnetron sputtering as an electrolyte layer for inorganic all-solid-state electrochromic devices.The ionic conductivity of LiPON films measured by electrochemical impedance spectroscopy was all approximately 10−6 S/cm, and the average optical transmittance characterized by UV–Vis spectroscopy was over 80%, indicating that the prepared LiPON films were suitable for electrochromic applications. Monoclinic electrochromic devices (ECDs) (ITO/NiOx/LiPON/WO3/ITO) with different LiPON thicknesses were fabricated and studied. It was found that the electro-optical properties of the ECDs could be significantly affected by the thickness and surface roughness of LiPON films. The ECDs demonstrated the best combination of optical contrast (68.4% at 560 nm), switching time (27s), and cycling stability (optical modulation degradation of 6.93% for 200 cycles) when the LiPON thickness was 450 nm. The above results not only shed lights on improving the interfacial properties of solid electrolytes, but also give directions for the performance enhancement of inorganic all-solid electrochromic devices.