1. School
of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798 Singapore, Singapore
2. Division
of Physics and Applied Physics, School of Physical and Mathematical
Sciences, Nanyang Technological University, 21 Nanyang Link, 637371 Singapore, Singapore
3. Singapore−Berkeley Research Initiative for Sustainable Energy, 1 Create Way, 138602 Singapore, Singapore
4. Energy Research Institute@NTU (ERI@N), Research TechnoPlaza, X-Frontier Block, Level 5, 50 Nanyang Drive, 637553 Singapore, Singapore