1. King Abdullah University of Science and Technology (KAUST), Division of Physical Sciences and Engineering (PSE), KAUST Solar Center (KSC), Thuwal 23955, Saudi Arabia
2. Department of Physics, The Chinese University of Hong Kong, New Territories, Hong Kong
3. Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640, China
4. Department of Chemistry, Imperial College London, 80 Wood Lane, London W12 0BZ, United Kingdom