1. International Joint Research Laboratory of New Energy Materials and Devices of Henan Province School of Physics and Electronics Henan University Kaifeng 475004 China
2. School of Civil Engineering and Architecture Henan University Kaifeng 475004 China
3. Beijing Institute of Nanoenergy and Nanosystems Chinese Academy of Sciences Beijing 100083 China
4. School of Materials Science and Engineering Georgia Institute of Technology Atlanta GA 30332‐0245 USA