An Overview of Metallic Nanowire Networks, Promising Building Blocks for Next Generation Transparent Conductors: Emergence, Fundamentals and Challenges SEDIGHEH PIRSALAMI, 1 SEYED MOJTABA ZEBARJAD, 1,2 and HABIB DANESHMANESH 1 1.—Department of Materials Science and Engineering, School of Engineering, Shiraz University, Shiraz 71348-51154, Iran. 2.—e-mail: mojtabazebarjad@shirazu.ac.ir Transparent conductors (TCs) have a wide range of applications in numerous electronic and optoelectronic devices. This review provides an overview of the emergence of metallic nanowire networks (MNNs) as promising building blocks for the next generation transparent conductors. The fundamental as- pects, structure–property relations, fabrication techniques and the corre- sponding challenges are reviewed. Theoretical and experimental researches suggest that nanowires with smaller diameter, longer length and higher as- pect ratio have higher performance. Yet, the development of an efficient synthesis technique for the production of MNNs has remained a challenge. The synthesis method is also crucial to the scalability and the commercial potential of these emerging TCs. The most promising techniques for the synthesis together with their advantages, limitations and the recent findings are here discussed. Finally, we will try to show the promising future research trends in MNNs to have an approach to design the next generation TCs. Key words: Transparent conductors, next generation, metallic nanowire networks INTRODUCTION Materials that are simultaneously electrically conductive and are optically transparent, the so- called transparent conductors (TCs), play an impor- tant role in many of advanced devices such as solar cells, 1 touch screens, 2 organic light emitting diodes (OLED), 3 sensors, 4 e-papers, 5 window defrosters, 6 antistatic coatings 7 and so on. An ideal TC is the one with the lowest amount of sheet resistance and highest transmittance. However, depending on the application, the required sheet resistance is in the range of <10 X/sq to 10 6 X/sq 2,8,9 but typically the transmittance needs to be ‡90%. 8,9 Transparent conductors were known at the end of the nineteenth century with thin metal films being the first example. 10 In spite of opacity in bulk form, metals in the form of thin films with thicknesses in the range of tens of nanometers are transparent. 8 As the thickness is further reduced, the trans- parency increases, which is accompanied by a dramatic increase in the electrical resistivity. This occurs when thickness becomes comparable to the electron mean free path due to electron scattering as predicted by the Fuchs-Sondheimer theory. 11 Transparent conductive oxides (TCOs) were recog- nized shortly after thin metal films. The first report on transparent conducting oxides was by Ba ¨ deker in 1907. 12 He reported that thin films of cadmium metal deposited in a glow discharge chamber could become transparent upon oxidation and still retain their electrical conductivity. Transparent conduc- tors based on transparent conductive oxides include semi-conducting oxides of indium, tin, zinc, and cadmium; impurity doped TCOs such as fluorine- doped zinc oxide (ZnO: F); ternary compounds such as zinc stannate (Zn 2 SnO 4 ) and multi-component oxides consisting of a combination of TCOs such as a (Received September 20, 2016; accepted March 20, 2017) Journal of ELECTRONIC MATERIALS DOI: 10.1007/s11664-017-5467-z Ó 2017 The Minerals, Metals & Materials Society