1. Institute for Solar Energy Systems, School of Physics, Sun Yat-Sen University, Guangzhou 510006, P. R. China
2. Guangzhou High-Tech Zone Institute for Energy Technology Co. Ltd., Guangzhou 510730, P. R. China
3. School of Materials Science and Engineering, Anyang Institute of Technology, Anyang 455000, P. R. China
4. School of Physics and Optoelectronic Engineering, Guangdong University of Technology, Guangzhou 510006, P. R. China