**1. Introduction**

Zinc oxide (ZnO) is a II-VI semiconductor group which has a wurtzite as the most stable compound structure and has unique physical and chemical properties. In physical properties, ZnO has a high thermal stability, which starts to melt and boil at 1975°C; in optical properties, it has a high transparency and a direct band gap at 3.4 eV, which can be tuned by doping several elements such as Al, Ga, or In [1]. ZnO also has a low resistivity, which is about 1–2 × 10−4 Ωcm [2], a high thermal stability, a high electrochemical coupling coefficient, and a high bonding energy (60 meV) [1]. Due to all these unique properties, ZnO becomes a promising material, which can be applied in many fields as a sensor, converter, catalyst, and even as an important part in solar cells. This study aims to review ZnO as a transparent conductive oxide (TCO) in solar cells.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
