Department of Materials Science and Engineering and ‡California NanoSystems Institute, University of California Los Angeles , Los Angeles, California 90095, United States.
ACS Nano. 2014 Mar 25;8(3):2804-11. doi: 10.1021/nn4065567. Epub 2014 Feb 14.
Solution-processed metallic nanowire thin film is a promising candidate to replace traditional indium tin oxide as the next-generation transparent and flexible electrode. To date however, the performance of these electrodes is limited by the high contact resistance between contacting nanowires; so improving the point contacts between these nanowires remains a major challenge. Existing methods for reducing the contact resistance require either a high processing power, long treatment time, or the addition of chemical reagents, which could lead to increased manufacturing cost and damage the underlying substrate or device. Here, a nanoscale point reaction process is introduced as a fast and low-power-consumption way to improve the electrical contact properties between metallic nanowires. This is achieved via current-assisted localized joule heating accompanied by electromigration. Localized joule heating effectively targets the high-resistance contact points between nanowires, leading to the automatic removal of surface ligands, welding of contacting nanowires, and the reshaping of the contact pathway between the nanowires to form a more desirable geometry of low resistance for interwire conduction. This result shows the interplay between thermal and electrical interactions at the highly reactive nanocontacts and highlights the control of the nanoscale reaction as a simple and effective way of turning individual metallic nanowires into a highly conductive interconnected nanowire network. The temperature of the adjacent device layers can be kept close to room temperature during the process, making this method especially suitable for use in devices containing thermally sensitive materials such as polymer solar cells.
溶液处理的金属纳米线薄膜是一种很有前途的材料，可以替代传统的氧化铟锡，成为下一代透明、可弯曲的电极。然而，到目前为止，这些电极的性能受到接触纳米线之间高接触电阻的限制；因此，改善这些纳米线之间的点接触仍然是一个主要挑战。现有的降低接触电阻的方法要么需要高加工功率、长处理时间，要么需要添加化学试剂，这可能会导致制造成本增加，并损坏底层衬底或器件。在这里，我们引入了一种纳米级的点反应过程，作为一种快速、低功耗的方法来改善金属纳米线之间的电接触性能。这是通过电流辅助的局部焦耳加热和电迁移来实现的。局部焦耳加热有效地针对纳米线之间的高电阻接触点，导致表面配体自动去除、接触纳米线焊接，以及纳米线之间的接触路径重新形成更理想的低电阻几何形状，以实现更好的线间导通。这一结果表明了在高度反应性的纳米接触中热和电相互作用的相互作用，并强调了纳米级反应的控制作为将单个金属纳米线转变为高导电性互联纳米线网络的一种简单而有效的方法。在这个过程中，相邻器件层的温度可以保持在接近室温，这使得这种方法特别适合用于包含热敏材料的器件，如聚合物太阳能电池。
