Investigation of Sputter-Deposited Thin Films of Lithium Phosphorous Sulfuric Oxynitride (LiPSON) as Solid Electrolyte for Electrochromic Devices

Lithium phosphorus sulfuric oxide nitride (LiPSON) prepared by radio frequency sputtering is investigated as a transparent solid lithium-ion conductor for use in all-solid-state electrochromic (EC) devices. The LiPSON layers are characterized by X-ray photoelectron spectroscopy (XPS) and their electrical characteristics are studied by temperature-dependent impedance spectroscopy. Half-cells of LiPSON deposited on tungsten oxide (WOx) in contact with 1 m LiClO4 in propylene carbonate are studied by electrochemical impedance spectroscopy (EIS) and spectroelectrochemical measurements by cyclic voltammetry and chronoamperometry. A significant influence of LiPSON deposition conditions on the EC characteristics of WOx is observed in the achievable transparency change, as well as the color impression in the bleached and colored state. Formation of a solid-electrolyte interface (SEI) is indicated that leads to poor EC performance with long switching times of 20-60 min. Appropriate deposition conditions for LiPSON are established that maintain a good EC activity of WOx. An all-solid-state EC device is assembled of WOx/LiPSON with vanadium titanium oxide as counter electrode and aluminum-doped zinc oxide as back contact. Temperature-dependent EIS and spectroelectrochemical measurements show that in such an all-solid-state stack, the detrimental contact resistance could be avoided and switching times of less than 60 s are achieved.