1. Graduate School of Sciences and Technology for Innovation, Yamaguchi University, 2-16-1 Tokiwadai, Ube-shi, Yamaguchi 755-8611, Japan
2. Ningxia Key Laboratory of Photovoltaic Materials, Ningxia University, Yinchuan 750021, PR China
3. Toray Industries, Inc. Advanced Materials Research Laboratories, 3-2-1 Sonoyama, Otsu 520-0842, Japan