1 Institute of Photovoltaics/Department of Materials Science and Engineering, Nanchang University, Nanchang, 330031, China. yaokai@ncu.edu.cn.
2 Department of Applied Physics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China. yaokai@ncu.edu.cn.
3 Department of Applied Physics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China.
4 Department of Materials Science and Engineering, City University of Hong Kong, Kowloon, Hong Kong, China.
5 Institute of Photovoltaics/Department of Materials Science and Engineering, Nanchang University, Nanchang, 330031, China.
6 Institute of Physical Engineering, Brno University of Technology, Technická 2, Brno, 616 69, Czech Republic.
7 Department of Applied Physics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China. aphhuang@polyu.edu.hk.
8 Laboratory for Nanophotonics, Department of Physics and Astronomy, Department of Electrical and Computer Engineering, Rice University, Houston, Texas, 77005, USA.
9 Department of Materials Science and Engineering, City University of Hong Kong, Kowloon, Hong Kong, China. dangylei@cityu.edu.hk.