1. Tsukuba Research Center for Interdisciplinary Materials Science (TIMS), Graduate School of Pure and Applied Sciences, University of Tsukuba; 1-1-1 Tennodai, Tsukuba Ibaraki 305-8573 Japan
2. Organic Thin-Film Solar Cells Group; Photovoltaic Materials Unit, National Institute for Materials Science (NIMS); 1-2-1 Sengen Tsukuba Ibaraki 305-0047 Japan