Enhanced electrocatalytic activity and electrochemical stability of copper(I) sulfide electrode electrodeposited on a Ti interlayer-coated fluorine-doped tin oxide substrate and its application to quantum dot-sensitized solar cells

Copper(I) sulfide (Cu₂S) films are deposited on 15 nm-thick Ti (Titania) interlayer-coated fluorine-doped tin oxide (FTO) substrates. This is performed using potentiodynamic electrodeposition at selective numbers of cycles (10−20) in the potential range of −0.7 V to −0.2 V (vs. Ag/AgCl), followed by sulfurization. The results of Cu₂S films on the FTO/Ti substrates are subsequently employed as counter electrodes for cadmium selenide quantum dot-sensitized solar cells (QDSSC). The Ti interlayer facilitates the Cu (copper) nucleation, during the Cu electrodeposition and leads to side-by-side packing of small Cu₂S nanosheets after sulfurization. In contrast, conventional Cu₂S grown on the FTO consists of a mixture of large and small Cu₂S nanosheets. The distinct nanostructure of the FTO/Ti/Cu₂S counter electrodes enhances the electrocatalytic activity and electrochemical stability comparing to those of FTO/Pt (Platinum) and FTO/Cu₂S films. This is due to the increased number of electrochemically active sites, fast ion transport in the Cu₂S nanosheets perpendicular to the substrate, and good adhesion to the Ti interlayer. The optimized FTO/Ti/Cu₂S electrode, deposited in 15 cycles, contributes to significantly increase the cell efficiency (4.11%) of the QDSSC, resulting in 140% and 35.2% performances improvements for the QDSSCs with the Pt (1.71%) and FTO/Cu₂S (3.04%) counter electrodes, respectively.