Investigation On Synthesis And Welding Of Silver Nanowires And Properties Of Their Transparent Electrodes

The rapid progress in flexible optoelectronic devices is bringing unprecedented revolution to our life.As one of the most essential components of optoelectronic devices,transparent electrodes have attracted many attentions from researchers.Metallic silver nanowires?AgNWs?with outstanding electrical conductivity,transparency and mechanical properties are regarded as the most promising candidate for today's flexible optoelectronics.However,how to enhance the optoelectronic performance of AgNWs transparent electrodes to widely meet demands of flexible optoelectronics remains still an issue to be solved urgently.Firstly,AgNWs are synthesized through a modified polyol method.CuCl₂ and strainless steel fiber as controlling agents are introduced to mediate the purity of AgNWs.NaBr as synergistically controlling agent is further added into the reaction system to adjust the diameter of AgNWs.Also,the length of AgNWs can be tailored via controlling the stirring speed during the reaction.Optoelectronic properties of transparent electrodes fabricated with AgNWs with different diameters and lengths are investigated.Secondly,nanowelding of AgNWs is performed through a photochemical process induced by HCl vapor.Under illumination of room light,HCl vapor and O₂ in the air act as an etching couple,which can drive Ag atoms to transfer from the bottom AgNW at the junction to the top one at room temperature.These Ag atoms epitaxially recrystallize with the lattice of the top AgNW as template,during which the junction of AgNWs is fused.The optoelectronic properties of AgNWs transparent electrodes is improved via the HCl vapor-induced photochemical nanowelding.Further,the welded AgNWs transparent electrode with a low sheet resistance of 15 ohm/sq and high transmittance of 85%can be achieved,and shows excellent heating,electromagnetic interference shielding and mechanical performance.Besides,in-situ chemical nanowelding of AgNWs is induced by N₂H₄ vapor.During the welding,silver atoms are generated via an in-situ redox process with silver oxide layer naturally formed on the surface of AgNWs as solder and N₂H₄ vapor as reductant,which can fuse the junctions of AgNWs through epitaxial recrystallization.The sheet resistance of the welded AgNWs transparent electrode drops five orders of magnitude?10⁷ ohm/sq-10² ohm/sq?with the original high transmittance of 96%maintained,which thereby results in a significant increase in optoelectronic properties up to five orders of magnitude(figure or merit:10^-3-10²).A high transmittance up to96%at sheet resistance of 77 ohm/sq and low sheet resistance of 18 ohm/sq at transmittance of 92%can be achieved via the N₂H₄ vapor-induced in-situ chemical nanowelding.Besides,this welding improves the stretchability,and shows healing ability.Further,the single-electrode triboelectric nanogenerator fabricated with the welded AgNWs transparent electrode displays a high transmittance of 95%,and possesses excellent electric output and sensing performance.Based on outstanding transparency,this nanogenerator can function as a tactile sensor to record the touch control of a smart phone.Lastly,nanowelding of AgNWs is realized through a photothermal process induced by UV.The common UVA light with the wavelength range from 320 nm to400 nm is selected as a light source to weld AgNWs at room temperature with the junction between AgNWs as the light-driven source of heat.This welding shows a lowering trend with the diameter of AgNWs increasing,and possesses self-terminating and self-limiting features.Finite-Difference Time-Domain is used to simulate and analyze the mechanism of the UV-induced photothermal nanowelding.After welding,the sheet resistance of AgNWs?diameter:30 nm?transparent electrode decreases three orders of magnitude?10⁵ ohm/sq-10² ohm/sq?with a high transmittance of 97%retained,which thus results in an significant enhancement in the optoelectronic properties up to three orders of magnitude?figure of merit:0.1-110?.The welded AgNWs transparent electrodes display enhanced mechanical flexibility,electromagnetic interference shielding effectiveness and heating performance,and are further fabricated into smart window,transparent heater and transparent triboelectric nanogenerator.The UV-induced nanowelding technology is easily integrated into a continuous roll-to-roll slot die process,which realizes mass production of flexible AgNWs transparent electrode with a low sheet resistance of 25 ohm/sq and high transmittance of 90%.Taken together,controlled synthesis of AgNWs can be performed via a modified polyol method.Also,the aforementioned nanowelding technologies are capable of lowering sheet resistance of AgNWs transparent electrodes,maintaining high transmittance,significantly reinforcing optoelectronic properties,and improving mechanical flexibility.Further,the welded AgNWs transparent electrodes with enhanced performance are widely applied in flexible optoelectronic devices.Therefore,this work can provide theoretical basis and technical support for controlled synthesis and welding of AgNWs,enhancement in the performance of AgNWs transparent electrodes and fabrication of high-performance flexible optoelectronic devices.