1. Department of Chemistry, Seoul National University, Seoul 151-747, Korea
2. Department of Materials Science and Engineering, Seoul National University, Seoul 151-742, Korea
3. Department of Polymer Engineering, Pukyong National University, Busan 608-739, Korea
4. Department of Material Science and Engineering and the Center for Advanced Molecular Photovoltaics (CAMP), Stanford University, Stanford, California 94305, United States