1. Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University (NTU), 21 Nanyang Link, 637371 Singapore.
2. School of Materials Science and Engineering, NTU, Nanyang Avenue, 639798 Singapore.
3. Energy Research Institute @NTU (ERI@N), Research Techno Plaza, X-Frontier Block, Level 5, 50 Nanyang Drive, 637553 Singapore.
4. Singapore-Berkeley Research Initiative for Sustainable Energy, 1 Create Way, 138602 Singapore.
5. Institute of Materials for Electronic Engineering II, Rheinisch Westfälische Technische Hochschule–Aachen, Sommerfeldstrasse 24, D-52074 Aachen, Germany.
6. Laboratory of Photonics and Interfaces, Department of Chemistry and Chemical Engineering, Swiss Federal Institute of Technology, Station 6, CH-1015 Lausanne, Switzerland.