1. Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
2. School of Microelectronics, Shandong University, No. 1500 Shunhua Road, Lixia District, Jinan, Shandong Province 250101, China
3. Key Laboratory for Renewable Energy, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China