The Stability of CdS QDSCs Based on Optimized MWCNs/CuS Counter Electrodes

Abstract

In order to enhance the stability of CdS quantum dot sensitized solar cells (QDSCs), the CdS quantum dots (QDs) sensitizer is loaded with ZnS QDs as a passivation layer and Pt counter electrode (CE) material is replaced by multiwall carbon nanotubes (MWCNTs) combined with CuS QDs. The microstructure of CEs is observed by SEM and TEM. The results show acid-treated MWCNTs can possess a larger specific surface area resulting in loading more CuS QDs. CuS QDs with uniform nanometer size are deposited on the external wall of acid-treated MWCNTs. The electrocatalytic activity of CEs is analyzed by electrochemical impedance spectroscopy (EIS) and Tafel curves. The results exhibit that the electrocatalytic activity of acid-treated MWCNTs improves after the introduction of CuS QDs. Under 24 h one-sun illumination, the electrocatalytic activity of Pt CEs decreases remarkably, even less than acid-treated MWCNTs/CuS QDs CEs. The photoelectric property of QDSCs is analyzed with J–V curves. The photoelectric parameters of QDSCs can be improved considerably after loading CuS QDs into acid-treated MWCNT CEs. Power conversion efficiency (PCE) of the QDSC with acid-treated MWCNTs/CuS QDs CE is lower than that of Pt CE based one, but after 24 h one-sun illumination, it does not change in comparison with sharp PCE degradation of the Pt CE based QDSC. The mechanism of improved QDSC stability is discussed systematically through optimizing the CEs.