The Research On Improved Carrier Transport Properties And Stability Of Silver Nanowire Transparent Electrode And Its Application

Metal-based flexible transparent conductors（TCs）with high transmittance,low sheet resistance（R_□）,and high flexibility are key and indispensable components of the new generation of flexible optoelectronic devices,which mainly include ultrathin metal films,metal nanowire networks,and metal grid.Among them,metal nanowire networks,especially silver nanowires（Ag NWs）,have a great potential to replace brittle indium tin oxide（ITO）transparent conductors and therefore have attracted a lot of attention in recent years.In a typical polyol reduction method for the synthesis of Ag NWs,the long-chain polyvinylpyrrolidone（PVP）is need to be introduced as a ligand/capping agent to produce anisotropic one-dimensional（1D）Ag NW structures.The Ag NW TCs with percolation threshold can be formed by spin coating or other methods.However,the TCs made from Ag NW networks have many problems such as uneven distribution of R_□,high contact resistance（R_c）,poor stability,roughness,and poor adhesion,which limit practical applications.To solve the above problems,the following research works have been carried out.1.Ag NWs with a high aspect ratio were synthesized via a modified polyol reduction method by using mixed halide salts（CuCl₂,Na Br）.In the reaction system,the average diameters of Ag NWs decrease from>100 nm to<50 nm by increasing the proportion of n（Br^-）to an Ag NW synthesis,resulting in increased aspect ratios from 482 up to 958.The growth mechanism of Ag NWs is revealed by morphological characterization of the reacted products at different times,and finally,Ag NWs with high purity were obtained.Ag NWs TCs with a high aspect ratio shows a lower R_□of 83Ω/sq at a transmittance of 90.31%,compared with that of Ag NWs TCs（R_□:121Ω/sq;T:90.32%）with a low aspect ratio.These excellent optical-electrical properties of Ag NWs TCs demonstrate the huge potential in the field of optoelectronic devices.2.To improve the conductivity of Ag NWs,the two-dimensional（2D）Ti₃C₂T_xnanosheet prepared by the chemical exfoliation method can wrap on Ag NWs to form a patch layer.The abundant functional groups,such as–F,–O,and–OH on Ti₃C₂T_xnanosheets,would provide strong interfacial interactions between Ti₃C₂T_xand the substrate,which produces additional conductive channels besides the two-crossed Ag NWs.The transparent heater made from the MA hybrid film,relative to their counterparts made from the Ag NW film,delivers much-improved heating performance,for example,higher heating temperatures（55.6°C）and heating rates（1.14°C/s）when a voltage of 5 V is applied.Therefore,MA composite films show promising applications for next-generation electronics.3.The dual functions of the removal of the PVP layer and self-limited welding can be achieved for a series of commonly used plasmas,e.g.,O₂plasma,H₂–Ar plasma（1:9 in volume）,and N₂plasma.Theoretical simulations reveal that the self-limited welding is caused by the focusing of light（emitted during plasma generation）at the NW/NW junctions,which thermally activates silver atoms and drives recrystallization therein.With a cleaned surface and welded nature,the plasma-treated Ag NW film shows largely improved conductivity and high flexibility,greatly facilitating its application as a high-performance flexible transparent heater（cycling stability,>40 cycles of heating/cooling;temperature rising rate,112°C within 30 s at 8 V）.Moreover,the plasma-treated Ag NW can also serve as a basic electrode for a stacked electron-only device of Ag NW film/8-hydroxyquinoline/Ag electrode,improving its current collection efficiency by 5.47 times.These results suggest that plasma treatment can greatly benefit the applications of Ag NW film.4.Iodine ion modification enables Ag NW film with improved carrier transport properties and stability as high-performance TC.Here we further explore a one-step I^-ion modification strategy to completely replace the PVP layer with an ultrathin,dense layer of I^-ions,which not only greatly diminishes the R_□of the Ag NW film itself and that at the interface of the Ag NW film and a functional layer（e.g.,a collect electrode）but also effectively isolates the approaching of corrosive species.Consequently,this strategy can simultaneously improve the carrier transport properties of the Ag NW film and its long-term stability,making it an ideal electric component in diverse devices.For example,the transparent heater and pressure sensor made from the I^--wrapped Ag NW film,relative to their counterparts made from the PVP-wrapped Ag NW film,deliver much-improved heating performance and pressure sensing performance,respectively.These results suggest a facile post-treatment approach for Ag NW thin film with improved carrier transport properties and long-term stability,thereby greatly facilitating its downstream applications.5.A cryo-transferred method is put forward to transfer Ag NWs with Na BH₄cleaning and light-enhanced Ostwald Ripening Welding（ONW）,greatly improving the carrier transport properties and adhesion of Ag NW networks with a substrate.The cryo-transferred method can temporarily make the NOA63 film transform from elastomer to a brittle glassy state with much higher dimensional contraction behaviors,greatly generating strong grip force and facilitating the complete transfer of Ag NWs.After the transition,the frozen Ag NWs–NOA63film can recover to a flexible state at room temperature.The prepared parallel electrodes as a collect electrode can be assembled with Ti₃C₂T_x/fiber active layers to construct the pressure sensor,which exhibits higher sensitivity of 97.73k Pa^-1than that of the pressure sensor made from PVP-wrapped Ag NW–NOA63parallel electrodes.Our research provides a feasible solution for the preparation of Ag NW transparent electrodes with high transmittance,high carrier transport,high flexibility,and long-term stability,which greatly facilitates the commercialization of Ag NWs transparent electrodes in the field of transparent heaters and pressure sensors.