Transparent conductors (TCs) are materials, which are characterized by high transmission of light and simultaneously very high electrical DC conductivity. These materials play a crucial role, and made possible numerous applications in the fields of electro-optics, plasmonics, biosensing, medicine, and “green energy”. Modern applications, for example in the field of touchscreen and flexible displays, require that TCs are also mechanically strong and flexible. TC can be broadly classified into two categories: uniform and non-uniform TC. The uniform TC can be viewed as conventional metals (or electron plasmas) with plasma frequency located in the infrared frequency range (e.g. transparent conducting oxides), or ultra-thin metals with large plasma frequency (e.g. graphen). The physics of the nonuniform TC is much more complex, and could involve transmission enhancement due to refraction (including plasmonic), and exotic effects of electron transport, including percolation and fractal effects. This review ties the TC performance to the underlying physical phenomena. We begin with the theoretical basis for studying the various phenomena encountered in TC. Next, we consider the uniform TC, and discuss first the conventional conducting oxides (such as indium tin oxide), reviewing advantages and limitations of these classic uniform electron plasmas. Next, we discuss the potential of single- and multiple-layer graphene as uniform TC. In the part of the paper dealing with non-uniform metallic films, we begin with the review of random metallic networks. The transparency of these networks could be enhanced beyond the classical shading limit by the plasmonic refractive effects. The electrical conduction strongly depends on the network type, and we review first networks made of individual metallic nanowires, where conductivity depends on the inter-wire contact, and the percolation effects. Next, we review the uniform metallic film networks, which are free of the percolation effects and contact problems. In applications that require high-quality electric contact of a TC to an active substrate (such as LED or solar cells), the network performance can be optimized by employing a quasi-fractal structure of the network. We also consider the periodic metallic networks, where active plasmonic refraction leads to the phenomenon of the extraordinary optical transmission. We review the relevant literature on this topic, and demonstrate networks, which take advantage of this strategy (the bio-inspired leaf venation (LV) network, hybrid networks, etc.). Finally, we review “smart” TCs, with an added functionality, such as light interference, metamaterial effects, built-in semiconductors, and their junctions.

中文翻译：

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透明导体物理学

透明导体 (TC) 是一种材料，其特点是光的高透射率和同时非常高的直流电导率。这些材料发挥着至关重要的作用，并使其在电光、等离子体、生物传感、医学和“绿色能源”领域的众多应用成为可能。现代应用，例如在触摸屏和柔性显示器领域，要求 TC 也具有机械强度和柔性。TC 可以大致分为两类：统一和非统一 TC。均匀的TC可以被视为等离子体频率位于红外频率范围内的常规金属（或电子等离子体）（例如透明导电氧化物），或具有大等离子体频率的超薄金属（例如石墨烯）。非均匀 TC 的物理学要复杂得多，并且可能涉及由于折射（包括等离子体）和电子传输的奇异效应（包括渗透和分形效应）导致的传输增强。该评论将 TC 性能与潜在的物理现象联系起来。我们从研究 TC 中遇到的各种现象的理论基础开始。接下来，我们考虑均匀 TC，首先讨论传统的导电氧化物（如氧化铟锡），回顾这些经典均匀电子等离子体的优点和局限性。接下来，我们讨论单层和多层石墨烯作为均匀 TC 的潜力。在论文处理非均匀金属薄膜的部分中，我们首先回顾随机金属网络。这些网络的透明度可以通过等离子体折射效应增强到超出经典阴影限制。导电性很大程度上取决于网络类型，我们首先回顾了由单个金属纳米线制成的网络，其中导电性取决于线间接触和渗透效应。接下来，我们回顾了没有渗透效应和接触问题的均匀金属膜网络。在需要 TC 与有源基板（例如 LED 或太阳能电池）高质量电接触的应用中，可以通过采用网络的准分形结构来优化网络性能。我们还考虑了周期性金属网络，其中主动等离子体折射导致非凡的光传输现象。我们回顾了关于这个主题的相关文献，并展示了利用这种策略的网络（仿生叶脉 (LV) 网络，混合网络等）。最后，我们回顾了具有附加功能的“智能”TC，例如光干涉、超材料效应、内置半导体及其结。