AgNWs Micromesh-based Flexible Transparent Electrode And Electrochromic Device: Fabrication And Property Study

Owing to the advantages of fast switching speed,large optical modulation and cost-effective,electronic switchable color-changing devices have broad application prospects in fields of information displays,intelligent windows,and military camouflage.However,due to the inherent brittleness of the traditional transparent conductive electrode such as.indium tin oxide（ITO）,it is still a great challenge to achieve highly soft color-changing devices.Silver nanowire（Ag NWs）based transparent electrode has attracted special attention due to their high electrical conductivity(6.3×10⁷S m^-1),high mechanical stability and adjustable photoelectric performance.Currently,Ag NWs transparent electrodes are mainly based on random conductive networks.Although high conductivity in this conductive network can be maintained,the nodes formed by the accumulation of Ag NWs would cause a strong scattering effect and generally lead to low transmittance and high haze of networks,which is not beneficial to the application of color-changing devices.In addition,high deformation（e.g.stretching and folding）of the random conductive network also leads to the fracture of Ag NWs,resulting in a decrease in the electrical conductivity in networks.Reasonable structural design of Ag NWs conductive network is an important way to achieve high-performance flexible transparent electrodes and color-changing devices.In this thesis,the free energy of the substrate surface was first adjusted to promote sprayed Ag NWs droplets generating stronger capillary flow than the Marangoni effect on the substrate,followed by the assembly of Ag NWs micromesh structure.Furthermore,the stretchable transparent conducting electrodes（STCEs）were prepared by embedding such Ag NWs micromesh into the substrate through a transfer strategy,which can achieve a good balance between electrical and optical properties,and maintain good electrical conductivity even under a stretched state of 100%.On this basis,such STCEs were then applied to polymer-dispersed liquid crystal（PDLC）and electrochromic（EC）devices with high performance.The details are as follows:（1）STCEs based on embedded Ag NWs micromesh structure.The fluorinated PDMS substrate was employed to ensure that the capillary flow generated by droplet evaporation was much stronger than the Marangoni flow.In this way,Ag NWs are driven to migrate from the center to the edge during droplet evaporation and self-assemble to form a micromesh structure.Then,a new PDMS was coated onto the surface of the Ag NWs micromesh,so that the Ag NWs micromesh is successfully transferred and embedded into the PDMS substrate.Such STCEs with embedded Ag NWs micromesh showed a sheet resistance of 19Ωsq^-1,and a transmittance of up to 88%at 550 nm.The STCEs with different sheet resistance and transmittance could be prepared by adjusting the dosage of spraying Ag NWs to meet the customized requirements.STCEs can also maintain good conductivity and good chemical stability（resistance increase less than 20%）after 100 h treatment in H₂SO₄with p H=1,KOH solution with p H=13 and 3.5%Na Cl solution.Moreover,the STCEs can still maintain 1.5 times the original sheet resistance when stretched to100%.After 1000 bending cycles,the conductivity is almost consistent with the initial state,and it has good folding and twisting stability,indicating good mechanical stability of STCEs.This is mainly due to the unique embedded Ag NWs micromesh than can enhance the binding force between Ag NWs and the substrate,and protects part of Ag NWs from oxidation.（2）Construction and characterization of highly flexible PDLC devices and EC devices.The above STCEs were treated by plasma method to enhance the surface free energy and uniform spread of PDLC.After UV curing PDLC layer on STCEs surface,the PDLC devices with the sandwich structure were then assembled.The PDLC devices showed excellent photoelectric performance,including fast switching speeds（less than 1 second）,large optical modulation（69%at 600 nm）,and superior mechanical stability（bending over 1000 cycles and stretching to 40%）.In addition,the device also showed tactile sensing function,high sensitivity,and fast response to pressure stimulation.In order to fabricate EC devices,we further deposited WO₃EC material on the surface of MXene/Ag NWs composite electrode,in which the introduction of MXene improved the electrochemical activity and EC uniformity of WO₃on STCEs.The obtained film showed excellent electrochromic performance(74%at 633 nm,coloring and bleaching speed were 14.5 s and 7.9 s respectively,and the coloring efficiency was 59.34 cm²C^-1).In addition,the EC devices were assembled by using this film as the electrochromic layer and Ag@Au core-shell nanowires（Au@Ag NWs）as the counter electrode,showing good electrochromic performance.This strategy provides a new idea for further research and development of high-performance flexible EC devices.