1. Ulsan Advanced Energy Technology R&D Center, Korea Institute of Energy Research, 44776Ulsan, South Korea
2. Department of Materials Science and Engineering, Korea University, 02841Seoul, South Korea
3. Photovoltaics Laboratory, Korea Institute of Energy Research, 34129Daejeon, South Korea
4. Department of Physics, Chungbuk National University, 28644Cheongju, South Korea
5. R&D Division, Jusung Engineering Co., Ltd., 17094Yongin, South Korea