1. College of Materials Science and Engineering & Institute of New Energy and Low-carbon Technology, Sichuan University, Chengdu 610064, P. R. China
2. Engineering Research Center of Alternative Energy Materials & Devices, Ministry of Education, Chengdu 610065, P. R. China
3. Department of Science and Technology Innovation Consultant on Foreign Cooperation, Tongwei Solar Co., Ltd., Chengdu 610299, P. R. China