LiPON thin films with high nitrogen content for application in lithium batteries and electrochromic devices prepared by RF magnetron sputtering

• Thorough study on electronic properties on LiPON films with high nitrogen content prepared by RF sputtering has been done.
• The optical properties of LiPON were studied and the possibility for using in electrochromic device is discussed.
• The deposition rate of LiPON films is around 14 nm/min instead of 1–5 nm/min usually reported in the literature.
• The methods for determination of composition are discussed.
• The correlation between composition, local structure and ionic conductivity is discussed.

Transparent amorphous lithium phosphorus oxynitride (LiPON) thin films with different thickness have been prepared by RF magnetron sputtering at a growth rate of 14 nm/min. The mean ionic conductivity of as-deposited LiPON films determined by impedance spectroscopy was 4.9 μS/cm at 22 °C with the activation energy of 0.55 eV. The electronic partial conductivity was measured to be 1.6 × 10− 6 μS/cm by recording the current–time curves at a constant voltage. The optical transmission of LiPON films were measured by UV–Vis/IR spectroscopy. The prepared LiPON films on silica glass substrate showed transmission higher than 80% in the visible light range. The complex refractive index and bandgap (~ 2.94 eV) were estimated by fitting the transmission data with the Tauc–Lorentz dielectric function model. The local structure of the film was investigated by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Both methods confirmed the incorporation of nitrogen in the matrix. Nitrogen is present in two different chemical environments, corresponding to P − N < PP and PNP. Inductively coupled plasma-optical emission spectrometry (ICP-OES) and Rutherford backscattering spectrometry (RBS) measurements showed that the composition of the LiPON film was Li3.13PO1.69N1.39. The high nitrogen content and low oxygen content appears to be responsible for the specific electrical and optical properties of the LiPON films.