1. Advanced Photovoltaics Research Center Korea Institute of Science and Technology (KIST) Seoul 02792 Korea
2. Department of Electrical Engineering Korea University Seoul 02841 Korea
3. Department of Materials Science and Engineering Korea University Seoul 02841 Korea
4. Department of Physics Ewha Womans University Seoul 03760 Republic of Korea
5. Electronic Materials Research Center Korea Institute of Science and Technology (KIST) Seoul 02792 Korea
6. Clean Energy Research Division Korea Institute of Science and Technology (KIST) Seoul 02792 Korea