Formation of ruthenium-dots on counter electrodes for dye sensitized solar cells

A 34 nm-thick ruthenium layer was deposited on a flat glass substrate by atomic layer deposition at low temperatures followed by the formation of self-aligned Ru micro or nano-dots by rapid thermal annealing for 30 seconds at 400°C. The resulting substrates were re-coated with another 34 or 69 nm-thick Ru layers by ALD at 250°C. Finally, the effective area of 0.45 cm² dye sensitized solar cell with a glass / FTO / TiO₂ / dye / electrode / (nano-dots Ru / Ru)/glass structure was fabricated. The microstructure was examined by field emission scanning electron microscopy and atomic force microscopy. The photovoltaic properties, such as the short circuit current density, open circuit voltage, fill factor, and energy conversion efficiency, were characterized using a solar simulator and potentiostat. FE-SEM confirmed that the 34 nm and 69 nm-thick Ru layers re-deposited by the second ALD process showed a 65% and 49% larger surface area, respectively, than the flat glass substrate due to the rearranged nano-dots. The ECE of the final DSSC was 2.62%, which was a 1.45 times larger than that of the 34 nm-Ru flat glass substrate. These results suggest that the efficiency of DSSCs can be improved by increasing the effective surface area of a counter electrode by low temperature ALD.