1. Renewable Energy Research Center, Fukushima Renewable Energy Institute, National Institute of Advanced Industrial Science and Technology (AIST), 2-2-9 Machiike-dai, Koriyama, Fukushima 963-0298, Japan
2. Research Center for Photovoltaics, National Institute of Advanced Industrial Science and Technology (AIST), Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan