1. Department of Physics; The University of Hong Kong; Pokfulam Hong Kong SAR
2. Department of Materials Science and Engineering; Shenzhen Key Laboratory of Full Spectral Solar Electricity Generation (FSSEG); Southern University of Science and Technology; No. 1088, Xueyuan Rd. Shenzhen 518055 Guangdong P. R. China
3. Department of Chemistry; The University of Hong Kong; Pokfulam Hong Kong SAR