Impacts of Reduced Graphene Oxide in CdS/CdSe Quantum Dots Co-sensitized Solar Cells

The introduction of various amounts of reduced graphene oxide (RGO) to CdS/CdSe quantum dots co-sensitized solar cells was investigated to enhance the light absorption and to promote the electron transfer. The characterization and comparison of optical and electrochemical properties as well as the performance of the resultant quantum dot-sensitized solar cells (QDSCs) with different amounts of RGO have been investigated systematically. The introduction of RGO demonstrated to enhance the light harvesting and consequently increase the short-circuit current density (Jsc). ZnS inserting between QDs and RGO can effectively block the charge recombination at the interface; however, the defects of RGO in the TiO2/QDs/ZnS/RGO photoanode still may accelerate the interface charge recombination in QDSCs and lead to a slight decrease of the open-circuit voltage (Voc). The balance between the light harvesting and charge recombination in RGO modified QDSCs is a key for achieving high power conversion efficiency (PCE). Finally, the CdS/CdSe/ZnS co-sensitized cell with modification RGO (3 min) achieved a high PCE of 5.28% (Jsc = 15.8 mA/cm2, Voc = 572 mV), more than 13% higher than that of 4.69% (Jsc = 13.7 mA/cm2, Voc = 602 mV) obtained for the cell without RGO.