Study On Preparation And Performance Of Composite Transparent Electrode Based On Silver Nanowire@Polyvinylpyrrolidone

Silver nanowires(AgNWs),as the most potential material in flexible transparent conductive films,have attracted much attention in the past ten years.So far,transparent electrodes based on AgNW have been widely used in many fields and have shown excellent performance.AgNW has many advantages compared to the traditional transparent conductive material-indium tin oxide,such as excellent mechanical flexibility;transparent conductive film can be prepared on a large scale through a low-cost process;and more importantly,the large-scale synthesis method of AgNW is quite mature.However,the prepared AgNW transparent electrode has high contact resistance due to the nano-gap or weak contact at the wire lap.The weak line-to-line contact also affects the mechanical flexibility of the AgNW film,because the simply overlapped AgNWs will slide when electrodes bent or stretched,resulting in a decrease in film conductivity or failure.In addition,because AgNW has an ultra-high specific surface area,its surface activity is extremely high,and the phenomenon of atom diffusion is serious under low temperature conditions.Therefore,the melting temperature of AgNW is much lower than that of bulk silver(961°C).In addition,AgNW has a variety of failure modes(such as chemical failure,thermal failure,and electron migration,etc.).Generally,Ag₂O particles grow on the surface of AgNW,and nanowires are broken or decomposed.The existence of this instability factors will seriously affect the reliability of metal nanowire devices,and have a great impact on the life span of AgNW-related electronic products.This article will study the contact resistance and stability of AgNW as a starting point.1.The line-to-line contact resistance in the AgNW film is a key parameter of electrical performance,and many studies have been carried out by predecessors to reduce the wire junction resistance.However,these methods require specific equipment or other materials as"solder",and adversely affect the AgNW transparent electrode or substrate.In this article,the systematic AgNW welding rule is perfected for the first time.In previous studies,Joule heating has been used to realize the welding of metal nanowires,but there is no report on specific welding rules.In this work,we have accomplished the general welding law.This law can tell researchers how to adjust the welding voltage and time to obtain the best welding effect,and can be widely used for electrical welding of a variety of conductive films.After processing by this method,the square resistance of the AgNW transparent electrode is reduced from 240?/sq to 27?/sq.Compared with the most common post-treatment method,heat treatment(square resistance is reduced from 240?/sq to 43?/sq),this method can achieve better results.Moreover,electric welding only has an effect on the line-to-line contact according to Joule's law(Q=I²Rt),and basically has no negative effect on other parts.Compared with the heat treatment method,the AgNW transparent electrode can be better protected.2.Core-shell structure can endow silver nanowire(AgNW)with excellent stability.However,non-industrial preparation process and bad dispersity of present passivation shell layer greatly hinder its application.Polymer shell materials can solve these problems,but no researchers have adopted them,because there is currently no method to overcome the conductivity limit of insulating polymers except for removing the polymer.Here,inspired by the tunneling effect of the scanning tunneling electron microscope,we report a tunneling current junction welding strategy that can simultaneously protect the polymer and overcome its conductivity limit:(1)The key to overcoming the conductivity limit is controlling the thickness of the polymer shell to generate tunneling current;(2)Since the contact resistance is much higher than the nanowire resistance,and Joule heat mainly accumulates inside the lap,fixed-point welding can be achieved,and only the polymerization inside the lap is removed The AgNWs are welded together,and the polymer in other locations is preserved.Based on this strategy and our perfect electric welding law,the silver@polyvinylpyrrolidone core-shell(Ag@PVP)nanowire film was welded,and the results show that this strategy is effective.In addition,the Ag@PVP film has high transmittance and conductivity(32.5?/sq,94%),indicating that the PVP shell hardly affects the photoelectric properties of the AgNW film.85°C/85%RH reliability test(30 days)exhibited that the PVP shell layer endowed AgNW with excellent stability.Finally,the effectiveness of optoelectronic device employing Ag@PVP as the electrode is comparable to those of device on indium tin oxide.