Enhanced electrochromic performance of tungsten oxide thin films with oxygen vacancy deposited on PET by RF magnetron sputtering

Electrochromic (EC) materials provide sustainable and innovative technologies for EC devices (ECDs), smart windows and optoelectronic applications. The optical transmissions of EC materials can be modulated by applied voltage onto them. Achieving high optical modulation and coloration efficiency are essential for EC devices grown on solid substrates such as glass, as well as for those grown on flexible substrates. WO3 films were deposited on indium tin oxide (ITO) coated polyethylene terephthalate (PET) substrates prepared by sequential growth of the each layer using RF magnetron sputtering with increasing deposition pressure. To get a clear perspective on the effects of oxygen contents within the films, the oxygen fraction in the total increasing deposition pressure was kept constant. The structural, optical and electrochromic properties of tungsten oxide films were investigated in detail. The WO3 films deposited on flexible PET substrates exhibited higher coloration efficiency along both visible and near IR regions as the deposition pressure was increased. It is shown that there is an optimal oxygen to argon partial pressure ratio to prepare the WO3 films with improved EC properties varying with the total sputtering pressure. The highest coloration efficiency obtained about 193.9 cm2/C at 862 nm for the oxygen deficient film deposited at 20 mTorr.