1. School of New Energy and Materials, Southwest Petroleum University (SWPU), Chengdu 610500, P. R. China
2. Institute of Photovoltaic, Southwest Petroleum University (SWPU), Chengdu 610500, P. R. China
3. Institute of New Energy Technology, College of Information Science and Technology, Jinan University, Guangzhou 510632, P. R. China
4. Tongwei Solar Co., Ltd., Chengdu 610200, P. R. China