1. Department of Material Science and Engineering; Korea University; 145 Anam-ro, Seongbuk-gu Seoul 136-701 Korea
2. Photovoltaic Development Team; Samsung SDI Co., Ltd.; Cheonan-Si 331-300 Korea
3. KU-KIST Green School, Graduate School of Energy and Environment; Korea University; 145 Anam-ro, Seongbuk-gu Seoul 136-701 Korea
4. Department of Physics; Kunsan National University; South Korea 54150 Korea