Fabrication Of High-performance Silver Nanowire Flexible Transparent Electrodes And Their Application In OLED

Flexible transparent electrode（FTE）is one of the key components in many flexible electronics,such as flexible displays,flexible solar cells,and flexible sensors,and it needs to be able to work steadily under certain deformation,including bending,twisting,stretching,and compression.The key factor affecting the performance of FTE is conductive material.Indium tin oxide（ITO）film is a commonly used material for processing transparent electrode.However,ITO film is not suitable for processing FTE due to its brittleness.Silver nanowire（AgNW）,with excellent conductivity,is cheap and AgNW network is extremely flexible,making AgNW being one of the best alternatives for ITO film.Despite its many advantages,AgNW network still has problems of high contact resistance and poor thermal stability,which make the prepared AgNW FTE difficult to reach the expected conductivity and service time.Therefore,the key technology to prepare high-performance AgNW FTE is the preparation of AgNW network with small contact resistance and high thermal stability.In this paper,it is proposed to deposit nanosolders at junctions to reduce the contact resistance of AgNW network,and TiO₂ protective shell is used to cover AgNW network to improve its thermal stability,and AgNW FTE with excellent photoelectrical performance and high flexibility is fabricated by embedding AgNW network on the surface of polymer substrate.Then,a flexible organic light-emitting diode（OLED）based on the AgNW FTE has been developed.Finally,the problem of low light extraction efficiency of the flexible OLED is successfully solved by adding light extraction structure on the surface of the AgNW FTE.A self-limited nanosoldering method is proposed to join the AgNW network.This method can deposit nanosolders at junctions,thus improving the conductivity of the AgNW network.As the self-limited nanosoldering method merely deposit nanosolders at junctions,this method has no influence on the transparency of the AgNW network.At a high transmittance of 89.3%,the sheet resistance of the AgNW network is dropped from 18.6 to 7.7 Ω/sq after self-limited nanosoldering.In addition,the deposited nanosolders can reduce the Joule heat generated by the AgNW network and reduce the chemical gradient from AgNW to junction,and thus improve the current stability of the AgNW network,ensuring that the AgNW network can work stably under a current stress of 75 m A/cm².AgNW@TiO₂ core-shell network is successfully prepared by means of thermal decomposition of TiO₂ sol,in which the AgNWs are wrapped by TiO₂ protective shell with continuous morphology and uniform thickness.The TiO₂ protective shell can inhibit the diffusion of silver atoms on the surface of AgNWs,so that the AgNW@TiO₂ core-shell network can work stably at 300 ℃,while the original AgNW network is quickly broken at 225 ℃.The shrinkage force generated by thermal decomposition of TiO₂ sol into TiO₂ protective shell can reduce the surface roughness of the AgNW network,weaken the light scattering of the AgNW network,and thus improve the transparency of the AgNW network.Additionally,this shrinkage force will squeeze the AgNWs,making them more tightly connected,thus reducing the contact resistance and improving the conductivity of the AgNW network.A high-performance AgNW FTE is prepared by embedding the AgNW network on the surface of polymer substrate,which has transmittance of 74.6%,sheet resistance of 6.2 Ω/sq,and surface roughness of 1.1 nm.Subsequently,a flexible OLED is fabricated on the surface of the AgNW FTE using spin coating and evaporation technologies.It is found that the AgNW FTE can eliminate the waveguide mode,so that the flexible OLED has high current efficiency（82.3 cd/A）and power efficiency（67.6 lm/W）.In addition,the current density of the flexible OLED is very low,and the decay rate of the organic emitting layer is slow,which makes the lifetime of the flexible OLED reaching at 420 min.Finally,AgNW FTE with light extraction structure is prepared by all-solution method.The light extraction structure can reduce the incident angle of light at the polymer substrate/air interface,avoid the total internal reflection of light,and improve the light extraction efficiency of the flexible OLED.After adding the light extraction structure on the surface of the AgNW FTE,the light extraction efficiency of the flexible OLED is improved from 28.0% to 38.4%,and its current efficiency and power efficiency are improved to 100.3 cd/A and 85.8 lm/W,respectively.In addition,after adding the light extraction structure,the luminescence spectra and the coordinates of Commission Internationale de L’Eclairage（CIE）of the flexible OLED are basically the same at different viewing angles,which is beneficial to the development of flexible OLED displays with a wide perspective.