Graphene-MoS₂ nanosheet composites as electrodes for dye sensitised solar cells

Replacing the platinum counter electrode in dye-senstized solar cells with a cheaper material has attracted much attention recently. Graphene, graphene oxide and other 2-dimensional materials have received significant attention. Here we demonstrate the dependence of device parameters on the thickness of counter electrodes formed from porous, disordered arrays of liquid-exfoliated graphene nanosheets. We find device efficiency to saturate at a counter electrode thickness of ∼ 400 nm. Such optimised counter electrodes can be improved further by adding MoS₂ nanosheets to the graphene electrode. By measuring the dependence of device parameters on the composition of mixed graphene/MoS₂ electrodes, we show that adding ∼ 10 wt% MoS₂ nanosheets to a graphene counter electrode improves performance and can result in a cell efficiency of∼ 95% of that achieved using a platinum electrode. This data is consistent with the MoS₂ nanosheets being somewhat better catalysts than the graphene nanosheets. However, the graphene nanosheets are required to render the electrode conductive. More detailed analysis suggests the better performance of the MoS₂ nanosheets to be mostly down to their smaller size.