Flexible quantum dot-sensitized solar cells employing CoS nanorod arrays/graphite paper as effective counter electrodes

We present a flexible solar cell which is composed of cobalt sulfide (CoS) nanorod arrays (NRAs) on graphite papers (GPs) (CoS NRAs/GP) as the counter electrode and CdS/CdSe quantum dot sensitized ZnO NRAs (CdS/CdSe@ZnO NRAs) as the photoanode. Orderly ZnO NRAs were directly fabricated on the flexible ITO/PET substrate by a hydrothermal method and CdS and CdSe quantum dots were subsequently deposited on them by chemical liquid deposition. CoS NRA/GP hybrid electrodes showed much higher electrocatalytic activity, higher exchange current density, and lower charge transfer resistance toward the reduction of S-x(2-) ions compared to Pt and GP electrodes and they exhibited superior performance when functioning as counter electrodes (CEs) in CdS/CdSe quantum dot-sensitized solar cells (QDSSCs), 400-500% better than that with Pt and GP as counter electrodes. An absolute energy conversion efficiency of 2.70% has been demonstrated for the QDSSC employing an optimized CoS NRA/GP hybrid electrode, which was relatively higher than those of the QDSSCs featuring Pt (0.52%) and GP (0.71%) CEs. This work not only provides a hybrid electrode with high catalytic activity for QDSSCs, but also demonstrates a cost-effective way to fabricate flexible electrodes that can be applied in dye-sensitized solar cells or super capacitors.