Low-Temperature Laser Synthesis of LiCoO₂ and WO₃ Films for Electrochromic Application

Abstract

The laser synthesis method is used to fabricate amorphous dielectric WO₃ films on fused silica and c-sapphire substrates at room temperature and thin LiCoO₂ films (thickness, 10–60 nm) on c-sapphire and silicon substrates. The films are intended for use as the key components of thin-film all-solid-state electrochromic cells based on flexible polymer substrates. The optical and electrophysical properties and surface morphology of the films prepared at room temperature are studied in relation to the type of subtrate and oxygen pressure used during growth process. Variation of the oxygen pressure has a marginal effect on the surface roughness of the WO₃ films, which is 4–5 nm. The type of substrate has almost no influence on the surface roughness of the LiCoO₂ films, which on average is 35 nm. Increasing the oxygen pressure inside the vacuum chamber leads to the formation of the WO₃ films with better light transmission characteristics in the entire considered range of 200–1000 nm. The transmittance of the LiCoO₂ films increases from 30 to 70% in the investigated spectral range of 300–1000 nm. The low-temperature laser synthesis is used in fabricating a WO₃-based solid state electrochromic cell. When a voltage of 2 V is applied, its transmittance in the spectral range of 300 to 900 nm decreases by 30% for 2 min.