[1] Tianjin Univ Technol, Sch Mat Sci & Engn, Tianjin Key Lab Photoelect Mat & Devices, Tianjin 300384, Peoples R China
[2] China Acad Civil Aviat Sci & Technol, Beijing 100028, Peoples R China
[3] Penn State Univ, Mat Res Lab, University Pk, PA 16802 USA