1. Fraunhofer Institute for Solar Energy Systems, Heidenhofstraβe 2, D-79110 Freiburg, Germany
2. Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
3. Department of Materials Science and Engineering, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul 136-713, South Korea
4. FUTURE-PV Innovation, Koriyama, Fukushima 963-0215, Japan
5. Kyoto University, Yoshida-Honmachi, Sakyo-Ku, Kyoto 606-8501, Japan