KrF excimer laser irradiated nanoporous TiO2 layers for dye-sensitized solar cells: Influence of laser power density

This paper reports the performance of dye-sensitized solar cells (DSSCs) with nanoporous TiO2 photoanodes irradiated by KrF excimer laser beams of various power densities. The laser induces surface remelting and solidification to create textures on the TiO2 layers. After laser irradiation, TiO2 also undergoes a phase transition from anatase to rutile; the amount of the transformed phase increases with the laser power density. For dye-anchored TiO2 layers, light absorption increases first and then decreases as the laser power density increases. The assembled cell efficiency, strongly correlated with the photocurrent density, also increases first and then decreases as the laser power density rises. This indicates that laser treatment creates surface textures on TiO2 that improve light trapping in the dye-anchored TiO2 photoanodes, thereby increasing the photocurrent level and cell efficiency. For high laser irradiation power density, the ablation of the TiO2 layer becomes significant, leading to a decrease in cell efficiency. The surface remelting and solidification process reduces the density of the surface recombination centers on TiO2, resulting in an increase of open-circuit voltage.