Low-Resistance Transparent Conductors Based on Co-Percolation in Hybrid Graphene/Nanowire Films

题目：基于混合石墨烯/纳米线薄膜共渗的低电阻透明导体非技术：该项目将研究一类新的低电阻透明导电电极，该电极基于二维（2-D）和一维（1-D）材料的组装，包括单层石墨烯和金属纳米线。一项整合良好的实验和建模工作将研究电导率和光传输特性作为材料参数的函数，包括纳米线密度和石墨烯晶粒尺寸。提出的研究将为材料系统的传导和接触特性提供新的理解，该材料系统可以提供优于氧化铟锡（ITO）的性能，使用更多的地球丰富的材料和物理优势，包括灵活性。所提出的工作的见解可以应用于先进的光伏器件，透明电路，发光二极管，显示器或探测器/成像仪。技术方面：该计划将研究一种新型的低电阻透明导电电极，该电极基于石墨烯/纳米线混合网络中的共渗导电。在大面积石墨烯层和金属纳米线网络中，导电是通过渗透进行的，高电阻晶界或纳米线结限制了薄片的电导率。混合石墨烯/纳米线系统可以通过渗透掺杂（金属纳米线桥接晶界）或共渗透（纳米线提供第二种耦合渗透路径，使一层的传输瓶颈被另一层网络桥接）显着降低薄片电阻。概念验证实验表明，在共渗极限下运行的混合网络中，在90%的光透射率下，可以实现20欧姆/平方的片电阻，并在几个月内观察到稳定的性能。在这个项目中，一个完整的实验和建模工作将解决两个主题。第一个主题将集中于理解在渗透掺杂和共渗透极限之间调整的混合石墨烯/纳米线网络的传导机制和结构与电子/光学性质之间的关系。第二个主题将集中于理解这些混合网络和“器件”层之间的接触特性，包括有机光伏器件或薄膜晶体管感兴趣的材料。本主题将透明导电电极应用于光伏和晶体管器件感兴趣的接触结构，以研究潜在的性能改进。该计划的智力优势包括探索石墨烯和金属纳米线的新型纳米结构2D-1D混合材料的传导和接触特性，以解决这些材料的基本限制。实验和建模工作的良好整合将探索复合材料的参数空间，以深入了解这种耦合系统中的传导性质，相关器件层的接触特性，以及改善薄片电阻与透明度关系的途径。除了标准的电学、光学和结构表征技术外，实验工作还将利用热反射成像来提供有关网络中电流路径和体积与结效应的信息。建模工作建立在理解无序系统中纳米级电子输运的独特能力以及纳米结构/有机光伏器件的基本模型之上。该计划的更广泛的影响包括一个综合教育和推广计划，旨在解决由于许多项目的跨学科性质而产生的纳米技术相关教育/培训方面的挑战，并旨在为来自代表性不足的群体的参与者提供机会。拟议的计划包括i)开发“Nanohub-U”课程的模块，可在全球范围内使用，ii)为本科生提供综合研究和专业发展经验，以及iii)以透明导电电极为重点的研究和技术研讨会。

Title: Low-Resistance Transparent Conductors Based on Co-Percolation in Hybrid Graphene/Nanowire FilmsNon-technical: The program will investigate a new class of low-resistance transparent conducting electrodes based on assemblies of two-dimensional (2-D) and one-dimensional (1-D) materials, including single-layer graphene and metal nanowires. A well-integrated experimental and modeling effort will investigate electrical conductance and optical transmission properties as a function of material parameters, including nanowire density and graphene grain size. The proposed research will provide new understanding of conduction and contact properties in a materials system which could provide performance superior to indium tin oxide (ITO), using more earth-abundant materials and physical advantages including flexibility. The insights from the proposed work can be applied to advanced photovoltaic devices, transparent circuitry, light emitting diodes, displays or detectors/imagers.Technical: The proposed program will investigate a new class of low-resistance transparent conducting electrodes based on co-percolating conduction in hybrid graphene/nanowire networks. In large-area graphene layers and metal nanowire networks, conduction is via percolation, with high-resistance grain boundaries or nanowire junctions limiting the sheet conductance. Hybrid graphene/nanowire systems can significantly reduce the sheet resistance, via percolation doping, in which metal nanowires bridge the grain boundaries, or, via co-percolation, in which the nanowires provide a second, coupled percolation path so that transport bottleneck of one layer are bridged by the other network. Proof of concept experiments have shown that sheet resistances of 20 Ohms/square can be achieved at optical transmittances of 90% in hybrid networks operating in the co-percolation limit, with stable performance observed over several months. In this program, a well-integrated experimental and modeling effort will address two themes. The first theme will focus on understanding the conduction mechanisms and relationship between structure and electronic/optical properties in hybrid graphene/nanowire networks tuned between percolation doping and co-percolation limits. The second theme will focus on understanding the contact properties between these hybrid networks and "device" layers including materials of interest for organic photovoltaic devices or thin-film transistors. This theme will apply the transparent conducting electrodes to contact structures of interest for photovoltaic and transistor devices in order to study potential performance improvements. The intellectual merits of the program include exploration of the conduction and contact properties in a new class of nanostructured 2D-1D hybrids of graphene and metal nanowires to address the fundamental limits of these materials. The well-integrated experimental and modeling efforts will explore the parameter-space of the composite to provide insights into the nature of the conduction in such coupled systems, contact properties to relevant device layers, and pathways toward improved sheet resistance versus transparency relationships. In addition to standard electrical, optical and structural characterization techniques, the experimental effort will utilize thermo-reflectance imaging to provide information on current pathways and bulk versus junction effects within the networks. The modeling effort builds on unique capabilities for understanding nanoscale electronic transport in disordered systems as well as fundamental models of nanostructured/organic photovoltaic devices. The broader impacts of the program include an integrated education and outreach program aimed at addressing challenges in nanotechnology-related education/training arising from the interdisciplinary nature of many of the projects, and aimed at providing opportunities for participants from under-represented groups. The proposed program includes i) development of modules for a "Nanohub-U" course, accessible worldwide, ii) integrated research and professional development experiences for undergraduates, and iii) a research and technology symposium focused on transparent conducting electrodes.