Highly Stable Stretchable Transparent Electrodes Based On Silver Nanowires

Stretchable transparent electrodes(STEs)with high performance are critical for the future fabrication of flexible and wearable electronics and optoelectronics.Silver nanowires(AgNWs)are characterized by their unique one-dimensional(1D)nanostructure and high conductivity.By depositing the conductive percolative network formed by AgNWs onto the elastomer substrate,it is possible to obtain STEs with low sheet resistance(Rs),high light transmittance(T),and a certain degree of endurance to tensile strains.However,for such AgNW-type STEs,there are inherent contradictions between their low Rs and high light T,as well as between low Rs and high stretchability.Additionally,in order to reduce the contact resistance at NW-NW junctions in the AgNWs conductive network,complicate post-processing processes are often required.Additionally,because AgNWs can be easily oxidized,the resulting electrodes show poor chemical and long-term use stability.This doctoral dissertation aimed to address the aforementioned issues by either(1)using 1D carbon nanotubes(CNTs)to composite with AgNWs,or(2)synthesizing silver@gold core-sheath nanowires(Ag@Au NWs)to develop AgNW-based STEs with high tensile strain endurance and high environmental stability with the help of a simple yet effective posttreatment process called capillary-force-induced welding.The main findings are summarized as follows:1.A theoretical model of capillary force was proposed in order to understand the relationship between capillary force(FAgNW-AgNW)and the diameter of AgNWs,and it was extended to the hybrid network of AgNWs and CNTs.The results indicated that when using AgNWs with larger diameter,bigger FAgNW-AgNW can be obtained.Additionally,the bigger the ratio of the diameters of the top and bottom AgNWs at a contact junction,the larger the FAgNW-AgNW that can be achieved.For the AgNW/CNT hybrid conductive network,using AgNWs with larger diameters and CNTs with the diameter close to that of AgNWs results in larger FAgNW-CNT.Larger capillary force can induce better cold welding between the nano buildingblocks.Additionally,the reliability of the theoretical model was verified by measuring the electrical resistance change before and after capillary-force-induced welding of a series of AgNW and AgNW/CNT films with varying diameters.2.A type of stable AgNW/CNT hybrid STE was fabricated through a vacuum filtration-transfer method coupled with the post-treatment process based on water vapor-induced capillary welding.The resultant STEs showed a Rs as low as 7.1Ωsq.-1,a T of 50.2%,and a small resistance increase of only 42%when uniaxially stretched to a strain of 580%.Additionally,the hybrid electrodes can tolerate equibiaxial stretching with a resistance rise of 100%at a strain of 200%,and can withstand at least 1500 stretching/releasing cycles with a resistance increase of 67%.The hybrid electrode’s oxidation resistance at room temperature was significantly higher than that of the AgNW-based electrode.Its resistance increases by less than 30%after 12 weeks of storage.In comparison,the resistance of the AgNW-electrode increased by 75%in the same period.The resultant AgNW/CNT hybrid STEs were tested as compliant electrodes for dielectric elastomer actuators(DEAs).The results indicated that these lightweight and highly tensile-strain-tolerant electrodes enabled the DEAs a low starting electric field(11.6 V μm-1),a high actuated areal deformation(190%),and stable actuation for at least 50 cycles.3.Three CNTs with varying diameters and three AgNWs with varying diameters and aspect ratios were used to fabricate a series of AgNW/CNT hybrid STEs with the help of capillary-force-induced welding caused by the mixed solvent of methanol and water.The effects of the size of the building blocks on the optical,electrical,and mechanical properties of the resultant STEs were studied in detail.The results indicated that AgNWs and CNTs with small diameters are beneficial for fabricating transparent electrodes with high light T and low haze;AgNWs with higher aspect ratios are advantageous for fabricating STEs with improved conductivity and mechanical stability;and the addition of an appropriate amount of CNTs can significantly improve the conductivity and tensile stability of AgNWs percolative network at the expense of some optical properties.Additionally,the closer the diameters of the AgNWs and CNTs are,the more favorable capillary welding is,which can further increase the conductivity and tensile endurance of STEs.The optimized AgNW/CNT hybrid STEs exhibited a low Rs of 8.70 Ω sq.-1,a T of 66.4%,a haze of 11.0%,and can endure uniaxial tensile strains up to 490%.A variety of alternating current electroluminescent(ACEL)devices based on such AgNW/CNT hybrid STEs were also successfully developed,showing uniform and stable luminescence.4.A novel type of Ag@Au NWs with a morphology resembling dual-headed matchsticks was synthesized via a chemical epitaxy deposition method using AgNWs as the template.By starting with such Ag@Au NWs,STEs with a T of 78.7%,a haze of 13.0%,a Rs of 13.5 Ω sq.-1 and a maximum tensile strain of 240%can be formed with the aid of capillary-force-induced welding.Due to the conformal and dense Au sheath,the resulting STEs displayed remarkable oxidation resistance,high-temperature resistance,and chemical/electrochemical stability.Additionally,non-enzymatic glucose biosensors were fabricated using such Ag@Au NW STEs.The electrocatalytic oxidation currents were proportional to glucose concentrations with a high sensitivity of 967 μA mM-1 cm2 and a detection limit of 125 μM over a detection range of 0.6 to 16 mM.The sensors can work stably under a 50%tensile strain and repeated bending cycles.Meanwhile,the sensors showed ultra-high reproducibility(relative standard deviation as low as 3.55%)and stability(retaining 93.6%of the original current response after 30 days),which is promising for practical wearable applications.