Preparation And Performance Of AgNWs-WO₃ Flexible Electrochromic Films

As a kind of smart material,an electrochromic film can rapidly and reversibly change its optical transmittance under the influence of an external electric field.The use of silver nanowires(Ag NWs)transparent electrodes instead of the original ITO electrodes in the electrochromic film not only satisfies the optical and electrical performance requirements,but also the silver nanowire electrodes have excellent mechanical properties,lower preparation costs and more mature The preparation process enables the electrochromic film to be applied in the fields of wearable devices,curved display,flexible optoelectronic devices,and complex surface spacecraft.In this paper,a series of work has been carried out on the design and preparation of electrochromic thin films based on silver nanowire electrodes.In this paper,firstly,the high purity and high aspect ratio silver nanowires were prepared by solvothermal method.The successful preparation of each experimental parameter in the reaction system,including heating temperature,reaction time,addition amount of nucleation control agent Na Cl,molecular weight of the morphology control agent PVP,purification method,and systematic characterization of the product were successfully performed.A one-dimensional silver nanowire with a length of 3-100 ?m,a diameter of 40-80 nm and a length-diameter ratio of 80-1600 is uniform and uniform in size.Silver nanowires transparent electrodes were prepared using medium-length silver nanowires with an average diameter of 50-60 nm and a length of 50-60 ?m.Two transparent electrodes,Ag NWs/Glass,Ag NWs/PET and Ag NWs/PC,were successfully fabricated on glass,PET and PC substrates by spin coating and drop coating methods,respectively.The experimental results show that the electrode prepared by spin coating method has poor surface uniformity and silver nanowires agglomeration,resulting in a large difference in optical transmittance and sheet resistance at different positions of the electrode,and it is difficult to meet the requirements;however,a drop coating method is used.The prepared three types of transparent electrodes have good uniformity.By changing the concentration of the dropped silver nanowires and the number of dropping drops of solution,a higher optical transmittance(above 80% at 550 nm)and a low sheet resistance were successfully prepared.(20 ?/sq.or less)Transparent electrode with optical and electrical properties close to that of ITO.Finally,in this paper,a layer of WO3 layer was deposited on the surface of two flexible silver nanowire transparent electrodes by electron beam evaporation method,and flexible electrochromic films with Ag NWs/PET-WO3 and Ag NWs/PC-WO3 structures were prepared.The 300 nm and 400 nm thick WO3 layer electrochromic films exhibited good electrochromic properties under a voltage window of-0.5 to 0.2 volt,and the optical modulation rate reached 80% or more.The film still has an electrochromic after 500 cycles.Color change performance,good cycle durability.In addition,the mechanical flexural properties of the film were tested and analyzed.It was found that the flexible electrochromic film with Ag NWs-WO3 structure had a certain flexibility,and the optical modulation rate was slightly reduced after a few cycles of the film bending.,but the electrochromic performance remains stable;but after a large number of bending cycles,the optical modulation rate of the film is obvious,and the electrochromic performance degradation such as cycle stability is severe.