1. College of Chemistry, Nankai University, Tianjin 300071, China
2. National Renewable Energy Laboratory, Golden, Colorado 80401, United States
3. Institute of New Energy Material Chemistry, Nankai University, Tianjin 300350, China
4. SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
5. T. J. Watson Laboratory of Applied Physics, California Institute of Technology, Pasadena, California 91125, United States