Electrochemically Deposited CoS Films as Counter Electrodes for Efficient Quantum Dot-Sensitized Solar Cells

In this study, we report on electrochemically deposited CoS onto ITO conducting glass substrates as counter electrodes for efficient quantum dot-sensitized solar cells (QDSCs). The CoS/ITO counter electrodes show remarkable electrocatalytic activity for the reduction of polysulfide compared to that of the CoS/ITO counter electrodes fabricated by chemical bath deposition (CBD) or the widely used thermal platinized FTO glass electrode. A CdS/CdSe based QDSC in combination with this type of counter electrode shows appreciated power conversion efficiency (PCE) of 5.2%, accompanied by 0.60 in fill factor under 1 sun illumination (100 mW cm−2 AM 1.5G), which is superior than that of CoS/ITO (fabricated by CBD) based cell (PCE 4.06%, FF 0.55) and Pt/FTO based cell (PCE 3.64%, FF 0.52). The augmented photovoltaic performance of the CdS/CdSe based QDSC may be attributed to a small charger-transfer resistance for the reduction of polysulfide on the counter electrode.