1. School of Materials and Energy, University of Electronic Science and Technology of China, 2006 Xiyuan Ave, West Hi-Tech Zone, 611731 Chengdu, Sichuan, P.R. China
2. Department of Energy Systems Engineering, Faculty of Engineering, Koforidua Technical University, P.O. Box KF 981, Koforidua, Ghana
3. School of Materials and Energy, University of Electronic Science and Technology of China, 2006 Xiyuan Ave, West Hi-Tech Zone, 611731 Chengdu, Sichuan, P.R. China, e-mail: litingshuai@uestc.edu.cn
4. Department of Energy Sciences, Faculty of Engineering, Lund University, P.O. Box 118, SE-221 00 Lund, Sweden