1. School of Materials Science and Engineering; Georgia Institute of Technology; Atlanta GA 30332-0245 USA
2. Department of Electrical Engineering; Columbia University; New York NY 10027 USA
3. National Renewable Energy Laboratory (NREL); Golden CO 80401 USA
4. Department of Mechanical Engineering; Columbia University; New York NY 10027 USA
5. Beijing Institute of Nanoenergy and Nanosystems; Chinese Academy of Sciences; 100083 Beijing China