Preparation And Application Of High Performance Ag Nanowires Transparent Electrode

Owing to the flourishing development of mobile smart devices, the transparent electrodes (TEs) market is booming. The dominant material used in TEs today is tin doped indium oxide (ITO). However, the scarcity of indium element leads to the tight supply of ITO. Furthermore, the ceramic nature of ITO, which is brittle and easily cracks, is unfavorable for its deposition and post-treatment processes. Thus, the next generation of cheap and high performance transparent electrodes such as Ag nanowires (NWs), carbon nanotubes, graphene and conducting ploymer have emerged rapidly. Up to now, Ag NWs TEs, which have lowest sheet resistance given the fixed transmittance, are the the most potential candidate to replace conventional ITO.It is widely believed that the geometry of Ag NWs such as length and radius are the decisive factor for the optoelectronic properties of the Ag NWs network TEs, such as sheet resistance and transmittance. However, the specific relationship between the geometry and the optoelectronic property is still unclear. In order to guide high performance Ag NWs TEs fabrication, this paper simulates the dependence of the optoelectronic properties on the geometry of Ag NWs, which provided the best parameters for Ag NWs synthesis and the TEs preparation. Basing on the Ag NWs TEs, a novel dual functional sensor was fabricated. The main results are as follows:The effect of the length, the radius and the number density of Ag NWs on the optoelectronic properties of the Ag NWs networks TEs under percolation behavior was calculated based on the conductivity of Ag NWs. Firstly, the critical lengths of sticks with random sites and three different distributions of random orientations were studied using MATLAB. For the highly efficient roll-to-roll process, the distributions under random sites and two random orientations was intensively studied. The results have showed that the connectivity between the sticks is best when the two random orientations are orthogonal. The sheet resistances of the Ag NWs TEs were simulated using the finite element software-COMSOL Multiphysics, and also fitted with the critical length using percolation theory. The sheet resistance will obey to the power law of the percolation theory, and there are two different value of the power exponent when the length or the number density changes. The transmittance of the Ag NWs TEs will reduce with radius increases given the fixed sheet resistance. When the radius of Ag NWs is less than100nm, the enhancement of the length of the Ag NWs will improve the optoelectronic properties of the TEs greatly, and the influence of the radius on the optoelectronic properties can be ignored. In addition, the effect of the contact resistance on the optoelectronic properties can be reduced effectively by using long Ag NWs. The radius of Ag NWs prepared by polyol process is less than100nm, so the ultralong Ag NWs are the key factor for high performance TEs fabrication.According to the simulation, the ultralong Ag NWs were synthesized through the optimized polyol process. The effect of the additives, such as FeCl3and CuCl2, on the distributions of the length and the radius of the Ag NWs were systematically studied. When FeCl3was added, all of the average diameters were less than80nm, and the length distributions were narrow with the maximum length of100μm. While for the CuCl2additive, the average diameter of Ag NWs increased with CuCl2concentration, and the length distributions were wide with the maximum length exceeding300μm. After a comprehensive analysis of the influence of the additives on the distributions of length, Ag NWs with the average length of143μm and the average diameter of223nm were successfully obtained by using Cu(NO3)2as the additive.High performance TEs with the transmittance up to93.3%and the sheet resistivity of16Ω/sq were assembled using ultralong Ag NWs. Room-temperature plasma was employed to enhance the conductivity of the Ag NWs TEs by simultaneously removing the insulating PVP layer coating on the Ag NWs and welding the junctions tightly, which resulted in the excellent performance of Ag NWs TEs with the FOM as high as471. Furthermore, we developed a general way to transfer as-fabricated Ag NWs network onto various substrates directly. The transferred TEs had good flexibility and stability.The monolithically integrated dual functional sensor was fabricated based on the high performance Ag NWs TEs, which can work in both modes for non-contacting and extended mechanical contacting detection. The Cm-based sensor as we demonstrated is a qualified candidate for this purpose that can sense proximity and pressure in one device and make a complete, continuous, precise response to overall physical process from approaching to touch, then to press with a fast response, high stability and high reversibility. Meanwhile, the good isolation of each pixel in the designed matrix structure leads to accurate spatial sensing and location identification.