Enhanced electrocatalytic activity of electrodeposited F-doped SnO₂/Cu₂S electrodes for quantum dot-sensitized solar cells

Copper sulfide (Cu₂S) films were deposited on F-doped SnO₂ (FTO) substrates via the electrodeposition (ED) of copper (Cu) nanoparticles followed by sulfurization. The Cu nanoparticles were deposited on FTO substrates for various ED times ranging from 10 to 30 min at a constant -0.4 V. The FTO/Cu films consisted of flower-like nanoparticles comprised of randomly-clustering nanoflakes. The Cu nanoparticles electrodeposited for 10 min (FTO/Cu (10 min)) were dispersed sparsely over the FTO substrate, whereas the FTO/Cu (20 and 30 min) provided increased coverage. Unlike FTO/Cu₂S (10 min), the FTO/Cu₂S (20 and 30 min) consisted of vertically-standing large Cu₂S nanosheets with numerous small nanosheets in between. This was attributed to the sufficient number of Cu seed nanoflakes, which not only facilitate ion transport of the redox couple but also increased the surface area, leading to significantly enhanced electrocatalytic activity. The quantum dot-sensitized solar cell (QD-SSC) with FTO/Cu₂S (20 min) exhibited a significantly improved cell efficiency of 4.58%, compared to those with Pt and FTO/Cu₂S (10 min). The QD-SSC with the FTO/Cu₂S (30 min) showed similar cell efficiency to that with the FTO/Cu₂S (20 min), despite the larger surface area because of its amorphous crystallographic structure offsetting the electrocatalytic activity.