Cuprous Sulfide@Carbon nanostructures based counter electrodes with cadmium sulfide/titania photoanode for liquid junction solar cells

The counter electrode (CE) is an integral component of a quantum dot sensitized solar cell (QDSSC), for it catalyzes the electrolyte reduction during cell operation. CEs: copper sulfide (Cu2S), Cu2S@graphene oxide (GO), Cu2S@reduced graphene oxide (RGO) and Cu2S@functionalized multiwalled carbon nanotubes (F-MWCNTs) except C-fabric are prepared. The five CEs are used in QDSSCs with a TiO2/CdS/ZnS film as the photoanode. The power conversion efficiencies (PCEs) of the cells are: Cu2S (4%), Cu2S@GO (5.69%), Cu2S@RGO (2.62%), Cu2S@F-MWCNTs (6.34%) and C-fabric (3.86%). Among these, the Cu2S@F-MWCNTs CE based QDSSC exhibits the highest PCE due to the high conductivity and high surface area of F-MWCNTs and the catalytic activity of Cu2S for sulfide reduction, which promotes electron transfer to the electrolyte. The Cu2S@F-MWCNTs CE shows a lower charge transfer resistance (Rct) for the oxidized sulfide species reduction, a better exchange current density and a higher current density for the electrolyte reduction at the CE/electrolyte interface compared to other CEs. F-MWCNTs also have a suitably poised Fermi level for accepting electrons with ease from the current collector. The same electrode also shows a higher catalytic activity and a greater flat band potential for hydrogen evolution reaction relative to the other electrodes. This study furnishes insights on how Cu2S@carbon nanostructures based electrodes are extremely effective as CEs for QDSSCs