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 fin 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 N (1.71%) and FTO/Cu2S (3.04%) counter electrodes, respectively.