* Corresponding authors

^a Department of Applied Physics, Research Institute for Smart Energy, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, P. R. China
E-mail: aphhuang@polyu.edu.hk

^b State Key Laboratory of Optoelectronic Materials and Technologies, Centre for Physical Mechanics and Biophysics, School of Physics, Sun Yat-sen University, Guangzhou, Guangdong Province, P. R. China
E-mail: luox77@mail.sysu.edu.cn