1. Institute of Solar Energy, and Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education) School of Physics and Astronomy Shanghai Jiao Tong University Shanghai 200240 P. R. China
2. Guosheng Energy Research Institute Xuzhou 221011 P. R. China
3. Huaneng Clean Energy Research Institute Beijing 102200 P. R. China
4. Huaneng Gansu Energy Development Co., Ltd. Lanzhou 730070 P. R. China
5. Research Center for New Energy Technology Shanghai Institute of Microsystem and Information Technology (SIMIT) Chinese Academy of Sciences Shanghai 200240 P. R. China