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Lithium phosphorus oxynitride (LiPON) film with high ionic conductivity, low electronic conductivity and high transparency in UV-VIS range offers the possible applications as electrolyte for optical devices, e.g. electrochromic device. In this work, the optical properties of LiPON are investigated by means of variable-angle spectroscopic ellipsometry (VASE) and optical transmission spectra. LiPON thin films with composition of Li3.13PO1.69N1.39 and ionic conductivity of 4.9 × 10−6 S cm−1 at room temperature were prepared by RF magnetron sputtering. Optical constants have been derived on multiple samples with film thickness from 400 to 2000 nm in the energy range of 0.58-5.5 eV. The optical bandgap ( Eg) of LiPON film is shown to be 3.07 eV by a Tauc plot. It is found that when E < Eg the Urbach exponential decay of absorption is observed. The Urbach tail width at room temperature is estimated to be 0.361 eV for the LiPON film. [ABSTRACT FROM AUTHOR]

Lithium silicon phosphorus oxynitride (LiSiPON) thin films with different compositions have been prepared by RF magnetron sputtering in N2 by using three targets xLi2SiO3 · (1 − x) Li3PO4 with x = 0.1, 0.3, and 0.5. Compared with LiPON, the electrical properties of LiSiPON have been improved by introducing silicon. LiSiPON films deposited from the target 0.5Li2SiO3 · 0.5Li3PO4 yield the highest ionic conductivity of up to 9.7 × 10−6 S cm−1 with an activation energy of only 0.41 eV. The main mechanism for increasing ionic conductivity is the enhancement of carrier mobility. By DC polarization measurements the electronic partial conductivity was found at least seven orders of magnitude smaller than the ionic conductivity. Linear voltammetry results showed that the LiSiPON films are electrochemically stable in contact with stainless steel in the voltage range of 0-6 V. The substitution of silicon for phosphorus in the film evidenced from X-ray photoelectron spectroscopy analysis indicated silicon in the film will create more abundant cross-linking structures Si-O-P and (P, Si)-N < (P, Si), hence created more Li+ conducting paths which favored the higher mobility of lithium ions and larger ionic conductivity. The optical bandgap was found to decrease with increasing silicon content. We demonstrate that the prepared LiSiPON films with their larger ionic conductivity and low electronic conductivity may serve as an alternative to LiPON for applications in high energy density and high voltage lithium batteries. [ABSTRACT FROM AUTHOR]