Study On W-doped NiO_x Electrochromic Thin Film And The Application In Inorganic All-solid-state Device

Elecrtochromic(EC)materials are able to change their optical properties reversibly by insertion/extraction of positive ions and electrons with an applied voltage.NiOx appears to be a good candidate as anode in devices due to good cyclic reversibility and high coloration efficiency.But the application of NiOx is still limited from various shortcomings such as low bleached state transmittance and the difficulty to match the lithium ion storage with cathodic electrochromic layer.It has been proved by previous researches that adding W into nickel oxide films can improve the electrochromic properties,but the related researches are not systemic enough.In most researches about Ni-W mixed oxide films,samples were prepared by magnetron co-sputtering at fixed Ar/O2 ratio.The effects of different oxygen pressure and working pressure are not systematically studied and co-sputtering is not available for large scale coating manufacture.Therefore,in this study,Ni Ox:W films were prepared by DC reactive magnetron sputtering from a Ni-W alloy target under different process conditions.The effects of the oxygen partial pressure and working pressure during depositing on structure,morphology,composition and properties were systematically studied.In addition,Li+ is one of the necessary substances involved in electrochromic chemical reactions.Lithiation is a process of introducing Li+ into devices.In this paper,we will find a suitable process of lithiation to prepare the inorganic all-solid-state electrochromic device.The the films are composed by the mixtures of NiO,Ni2O3,WO3.With the increasing of oxygen flow during depositing,WO3 content increases,and the deposition rate and the size of grains decrease.Because more NiO are converted into Ni2O3,the increasing of oxygen partial pressure breaks the crystallinity,and optical transmittance decreases.The lattice constant of NiO increases because of the replacement between Ni2+ and W6+.The optical constants and optical band gap increase when adding more O2 during depositing.As the working pressure rises,the content of NiO in the sample increases,but the NiO with fcc structure changes to be amorphous state,and the crystallization degree of the film decreases.A more loose surface is observed with the increasing of working pressure.The optical transmittance increases because the increasing content of NiO and the decreasing of film density.Optical band gap obtained by calculation,refractive index and extinction coefficient obtained by SE fit,increase with the increasing of working pressure.The degree of lithiation has a significant influence on the driving voltage,coloration efficiency and optical modulation of the device.The inorganic all-solid-state electrochromic device FTO/LiyWO3/electrolyte/W-doped NiOx/ITO has good optical modulation of 56.3% with Tbleached=60.2% and Tcolored=3.9% at wavelength 550 nm.The coloration efficient is 1.54 cm2/C.