1. Green Energy Research Division, Daegu Gyeongbuk Institute of Science and Technology (DGIST); Daegu 711-873 Republic of Korea
2. Research Institute of Advanced Energy Technology; Kyungpook National University; Daegu 702-701 Republic of Korea
3. Department of Physics; Yonsei University Seoul; 120-749 Republic of Korea
4. Organic Nanoelectronics Laboratory, Department of Chemical Engineering; Kyungpook National University; Daegu 702-701 Republic of Korea