Dye-sensitized solar cells employing laser patterned counter electrodes

In order to enhance the energy conversion efficiency by increasing the surface area of the counter electrode (CE), we employed different substrates with the flat glass, FTO (fluorine-doped tin oxide), and laser patterned FTO. Ruthenium (Ru) films with thicknesses of 34 and 46 nm were deposited by atomic layer deposition (ALD) on each substrate. In this way, the dye sensitized solar cell (DSSC) device with an area of 0.45 cm² with a glass/FTO/blocking layer/TiO₂/N719(dye)/electrolyte/Ru/substrate structure was prepared. The microstructure of the CE was investigated with FE-SEM, and the photovoltaic properties were characterized by cyclic voltammetry (CV), impedance spectroscopy (EIS), and current-voltage (I-V) measurement. When we assumed the surface morphology as the array of a pyramid (width 0.24, length 0.24, and height 0.14 μm), we determined the surface area of the substrate of the flat glass, FTO, and laser patterned FTO as 1.36 × 10⁸, 2.32 × 10⁸, and 2.56 × 108 μm², respectively. CV and impedance results revealed an increase in catalytic activity and a decrease in interface resistance with increasing Ru thickness and surface area. When the Ru thickness was 34 nm (and 46 nm), the energy conversion efficiency of each substrate was 1.55% (1.96%), 2.62% (2.92%), and 2.95% (3.32%), respectively. These results suggest that increasing the Ru catalytic layer thickness and surface area of the CE contributed to increasing the efficiency. Moreover, increasing of surface area through laser patterning was more suitable for increasing the efficiency than the conventional flat glass, and FTO substrates.