1. School of Materials Science and Engineering Nanyang Technological University (NTU) Singapore Nanyang Avenue 639798 Singapore
2. Singapore-Berkeley Research Initiative for Sustainable Energy (SinBeRISE) 1 Create Way Singapore 138602 Singapore
3. Department of Materials Science and Engineering University of California Berkeley Berkeley CA 94720 USA
4. School of Physical and Mathematical Sciences Nanyang Technological University, Singapore Singapore 637371 Singapore