1. Konkuk University-Fraunhofer ISE Next Generation Solar Cell Research Center (KFnSC), Konkuk University, Seoul 143-701, South Korea
2. Department of Mechanical and Aerospace Engineering, University of California at San Diego, La Jolla, California 92093, USA
3. Department of Chemistry, Konkuk University, Seoul 143-701, South Korea
4. Research Institute for Solar and Sustainable Energies (RISE), Gwangju Institute of Science and Technology, Gwangju 500-712, South Korea