1. Institute of New Energy Technology College of Information Science and Technology Jinan University Guangzhou 510632 China
2. Department of Physics Tianshui Normal University Tianshui 741000 China
3. School of Chemical Engineering and Light Industry Guangdong University of Technology Guangzhou 510006 China
4. IEK-5 Photovoltaik Forschungszentrum Jülich GmbH 52425 Jülich Germany