1. School of Materials Science and Engineeringand Research Institute for Solar and Sustainable Energies; Gwangju Institute of Science and Technology; Gwangju 500-712 South Korea
2. Devices and Displays Research Laboratory; Chung-Ang University; Seoul 156-756 South Korea
3. School of Electrical and Electronics Engineering; Chung-Ang University; Seoul 156-756 South Korea
4. School of Electrical and Electronics Engineering; Yonsei University; Seoul 120-749 South Korea
5. School of Chemical Engineering; Sungkyunkwan University; Suwon 440-746 South Korea
6. School of Advanced Materials Science and Engineering; Sungkyunkwan University; Suwon 440-746 South Korea