6. Qingli Huang, Fan Li, Yun Gong, Jianheng Luo, Shize Yang, Yanhong Luo, Dongmei Li, Xuedong Bai, and Qingbo Meng, Recombination in SnO2-Based Quantum Dots Sensitized Solar Cells: The Role of Surface States, JOURNAL OF PHYSICAL CHEMISTRY C 117, 10965 (2013).