1. School
of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore
2. Division of Chemistry
and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore
3. Physical Sciences and Engineering Division, Solar and Photovoltaics
Engineering Research Center, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia
4. Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, P. R. China