Optimizing multi-walled carbon nanotubes as a low-cost and highly electrocatalytic counter electrode for QDSCs

Abstract

The development of multi-wall carbon nanotubes (MWCNTs) counter electrodes (CEs) is limited due to its poor electrocatalytic activity in quantum dot sensitized solar cells (QDSCs). In this work, nanographite and CuS quantum dots (QDs) are introduced into acid-treated MWCNTs to form 3D structural composite CE for the purpose of improving the catalytic activity. The morphology and microstructure of CEs are observed with SEM and TEM images. Either the introduced nanographite or CuS QDs have attached to MWCNTs, which makes composite CE in the higher specific surface area. The electrical property and catalytic activity of CEs is analyzed through EIS and Tafel curves. The result shows that catalytic activity of MWCNTs CEs can be optimized through introducing either nanographite or CuS QDs to increase active sites. And the catalytic activity of nanographite-based CE is worse than that of CuS QDs-based one, whose performance is close to that of Pt CE in QDSCs. The photovoltaic parameters of QDSCs based on different CEs are investigated through J-V curves. Even if the power conversion efficiency (PCE) of QDSCs with the Pt CE is slightly higher than that of MWCNTs composite, the short circuit current density of cell with nanographite/MWCNTs composite CEs (10.510 mA cm−2) is higher than that of Pt CE (10.222 mA cm−2) and the open-circuit voltage of cell of CuS QDs/MWCNTs CEs (0.874 V) is higher than that of Pt CE (0.756 V). CuS QDs/MWCNTs composite can substitute Pt material commercially as a low-cost and high efficient CEs in QDSCs.