Study On Flexible Electrochromic Devices Based On The Novelty ITO-Free Transparent Conducting Film

Electrochromism?EC?is defined as a phenomenon that the optical properties and colors dynamic changed under applied potential accompanied by reversible insertion/de-insertion of ions.EC has many advantages,such as rich color change,fast response time,high optical contrast,bi-stability,low energy consumption and no blind angle.More importantly,the color change state of EC can be easily adjusted by the user according to environmental conditions and self-like preferences.Therefore,it shows extremely promising applications in smart windows,adjustable mirrors and displays.Nowadays,developing novel flexible and multifunctional electrochromic devices?ECDs?has becoming more attractive.However,economic,large-scale,and reliable fabrication of such devices with high performance still faces some difficulties.The traditional ECDs structure comprises three superimposed layers?EC film,electrolyte,and ion-storage film or complementary EC film?positioned between two transparent conductors.This complicated layered structure not only increases the manufacturing cost because of the assembling process but also introduces multiple interfacial layers that could impede the ion transportation and thus reduce the device performance.In addition,the development of flexibility lies in the development of flexible transparent conductor.While the most popular transparent conductor used in ECDs is ITO conductor,which restrains the developing of flexible devices due to the problems of Indium scarce,high cost and brittleness.Finally,functional materials with excellent overall performance are still lacking.To solve the above three problems,we designed a dielectric-metal-dielectric film,which can be prepared by electron beam deposition method at room temperature.And WO₃,MoO₃ and NiO materials were studied by doping to improve the properties due to abandunt charge transfer and ion diffusion.The main contents and results are as follows:?The highly efficient rigid and flexible dual-functional indium-free films have been achieved by utilizing the mixed MoO₃-WO₃ as the dielectric layer for the first time.The effects of different doping concentrations on the structure and properties of the films were investigated.The best mixed film displayed good overall performance,with a low sheet resistance of 9.4??^-1,high average transmittance of 77.4%,strong and broadband optical modulation in visible light range,fast color switching time2.7/4.1 s,high coloration efficiency(70 cm² C^-1),as well as good long-term cycle stability.When used as a flexible film,it still has outstanding mechanical and electrochemical stability.These improved EC performances can be attributed to the increased electron intervalence transition together with the fast charge-transfer and ion-diffusion dynamics.The present study could provide an alternative route to improve EC performance for tungsten and molybdenum oxide materials and the demonstrated method could also be extended to other material system for adjusting the photoelectric performance.?For the first time,ion doping was introduced into the DMD structure.Pre-doped LiF/WO₃ was used as the dielectric material to improve the comprehensive performance of the dual-functional indium-free films.The EC response band can be easily adjusted by the change of the doping content.Moderate doping relieved the ion?trapping?phenomenon and the film can completely restored to original state.This laminated film simultaneously performed transparent conductive and EC functions,behaving with a high average transmittance of 80.1%,low sheet resistance of 9.4??^-1,as well as high optical constrast of 38.4%,excellent coloration efficiency of 157.3cm² C^-1,fast response time of 3.9/3.1 s and superior bending stability.These improved EC performances can be attributed to the good interface bonding,low inner resistance,high electrochemical activity and fast charge transfer and ion diffusion.The present study demonstrated that ion doping is an effective way to improve EC performance.?Transparent,conductive,and ITO-free NiO/Ag/NiO?NAN?electrodes,which combined excellent electrochromism and supercapacitance,were successfully fabricated by an easy one-step electron-beam deposition method at room temperature.The present study may provide a simple and effective way to combine EC performance,capacitive behavior,and transparent conductivity into one device,which could intuitively monitor the energy storage level by color changes.The film behaves with a good visible light transparency over 70%,high conductivity of 9.4??^-1,and superior EC cycling stability,as well as excellent electrochemical performances including record coloration efficiency 76.6 cm² C^-1,high specific capacitance 364.0 F g^-1@2 A g^-1,good rate capability,and great cycling stability?nearly unchanged after800 cycles?.These superior multi-properties can be attributed to high conductivity and good interfacial contact together with rapid electrochemical reaction kinetics.