1. Institute for Clean Energy & Advanced Materials School of Materials and Energy Southwest University Chongqing 400715 P. R. China
2. Beijing Key Laboratory of Photoelectronic/Electrophotonic Conversion Materials Key Laboratory of Cluster Science Ministry of Education School of Chemistry and Chemical Engineering Beijing Institute of Technology Beijing 100081 P. R. China
3. School of Physical and Mathematical Sciences Nanyang Technological University 21 Nanyang Link Singapore 637371 Singapore