1. Department of Electrical Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
2. Guangdong Provincial Research Center on Smart Materials and Energy Conversion Devices Guangdong Provincial Key Laboratory of Functional Soft Condensed Matter School of Materials and Energy Guangdong University of Technology, Guangzhou 510006, China
3. Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, USA