Selenization of Cu2ZnSnS4 Enhanced the Performance of Dye-Sensitized Solar Cells: Improved Zinc-Site Catalytic Activity for I3–

Cu2ZnSnS4 (CZTS) and Cu2ZnSn(S,Se)4 (CZTSSe) as promising photovoltaic materials have drawn much attention because they are environmentally benign and earth-abundant elements. In this work, the monodispersed, low-cost Cu2ZnSnS4 nanocrystals with small size have been controllably synthesized via a wet chemical routine. And CZTSSe could be easily prepared after selenization of CZTS. When they are employed as counter electrodes (CEs) for dye-sensitized solar cells (DSSCs), the power conversion efficiency (PCE) has been improved from 3.54% to 7.13% as CZTS is converted to CZTSSe, which is also compared to that of Pt (7.62%). The exact reason for the enhanced catalytic activity of I3– is discussed with the work function and density functional theory (DFT) when CZTSSe converted from CZTS. The results of a Kelvin probe suggest that the work function of CZTSSe (5.61 eV) is closer to that of Pt (5.65 eV) and higher than that of CZTS, which matched the redox shuttle potential better. According to the theory calcula...