Research Article In and Ga Codoped ZnO Film as a Front Electrode for Thin Film Silicon Solar Cells Duy Phong Pham, 1 Huu Truong Nguyen, 2 Bach Thang Phan, 2,3 Thi My Dung Cao, 3 Van Dung Hoang, 2 Vinh Ai Dao, 1 Junsin Yi, 1 and Cao Vinh Tran 2 1 College of Information and Communication Engineering, Sungkyunkwan University, 300 Cheoncheon-dong, Jangan-gu, Suwon 440-746, Republic of Korea 2 Laboratory of Advanced Materials, University of Science, 227 Nguyen Van Cu Street, 5th District, Ho Chi Minh City 70000, Vietnam 3 Faculty of Materials Science, University of Science, 227 Nguyen Van Cu Street, 5th District, Ho Chi Minh City 70000, Vietnam Correspondence should be addressed to Junsin Yi; yi@yurim.skku.ac.kr and Cao Vinh Tran; tcvinh@hcmus.edu.vn Received 21 October 2014; Accepted 7 December 2014; Published 28 December 2014 Academic Editor: Markus R. Wagner Copyright © 2014 Duy Phong Pham et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Doped ZnO thin flms have attracted much attention in the research community as front-contact transparent conducting electrodes in thin flm silicon solar cells. Te prerequisite in both low resistivity and high transmittance in visible and near-infrared region for hydrogenated microcrystalline or amorphous/microcrystalline tandem thin flm silicon solar cells has promoted further improvements of this material. In this work, we propose the combination of major Ga and minor In impurities codoped in ZnO flm (IGZO) to improve the flm optoelectronic properties. A wide range of Ga and In contents in sputtering targets was explored to fnd optimum optical and electrical properties of deposited flms. Te results show that an appropriate combination of In and Ga atoms in ZnO material, followed by in-air thermal annealing process, can enhance the crystallization, conductivity, and transmittance of IGZO thin flms, which can be well used as front-contact electrodes in thin flm silicon solar cells. 1. Introduction Tin flm silicon solar cells (TFS-SCs) have received much attention due to their advantages such as fexibility, large area deposition, and low-cost manufacturing [1–3]. Up till now, despite the many advantages of thin flm solar cells, their low efciency is still a drawback that must be improved. In the recent years, much efort has been put in enhancing TFS- SC efciency by many diferent ways [4–6]. One of these is to improve the quality of transparent conducting oxide (TCO) electrode layer, an integral part in the structure of thin flm solar cells [7]. TCO electrode layer usually plays an essential role as a front electrode and as a part of the backside refector. Upon use as front electrode for hydrogenated microcrystalline (c-Si:H) or amorphous/microcrystalline tandem (a-Si:H/c-Si:H “micromorph”) TFS-SCs in order to improve cell efciency, TCOs are required to have both a high transparency in visible as well as near-infrared (NIR) region, where the solar cell is operating, and a high electrical conductivity [8]. Unfortunately, these two characteristics depend adversely on each other. For TCO electrodes, the conductivity substantially depends on the carrier concen- tration and mobility. Te high conductivity of TCO flms normally desires a high carrier concentration, caused by intrinsic defects or external doping. Currently, the carrier concentration in well-developed TCOs is in the range of 10 20 -10 21 cm −3 . Tese high values induce a strong decrease in the transmittance in NIR region due to the free-carrier absorption so that these TCOs are not suitable for front transparent electrodes in solar cells [9]. Te combination of high conductivity and high transparency in both visible and NIR region is a key issue for TCO material and the enhancement of carrier mobility of TCO is a way of attaining this goal [10]. Among TCO thin flms, n-type doped ZnO thin flms have gained much interest in recent years due to their low resistivity, high transmittance, nontoxicity, good stability in hydrogen plasma processes, and resource availability [11, 12]. Hindawi Publishing Corporation Advances in Condensed Matter Physics Volume 2014, Article ID 971528, 7 pages http://dx.doi.org/10.1155/2014/971528