Electrodeposition of ZnO for Application in Dye-sensitized Solar Cells

ZnO has been electrodeposited from 0.5 M Zn(NO3)(2) at pH 4.5 with and without polyethylene glycol (PEG) as additive. Cyclic voltammetry on FTO substrates reveals two electrochemical regimes, where reduction of nitrate and water are rate determining, respectively. ZnO films were galvanostatically electrodeposited as a function of the deposition current density: at low current densities, where nitrate reduction is rate determining, highly crystalline ZnO films were obtained, whereas amorphous ZnO films were obtained at higher current densities, where water reduction dominates. The amorphous films transform to crystalline ZnO upon sintering, and SEM images show that the presence of PEG results in a homogeneous film morphology. The films were used for the fabrication of dye-sensitized solar cells (DSSCs), resulting in solar cell conversion efficiencies of up to 1.4% for non-sintered ZnO films deposited at low current density (without PEG), while the best cells were obtained with films electrodeposited from the plating bath with 0.15 mM PEG with efficiencies of up to 1.8% for sintered films prepared at higher current density. These results illustrate that the presence of PEG in the plating bath optimizes the film morphology and, hence, the performance of ZnO-based dye-sensitized solar cells.