Excimer laser surface treatment on TiO2 nanoporous layers for dye-sensitized solar cell application

This thesis discusses the characteristic parameters of dye-sensitized solar cells (DSSCs) made with KrF exicmer laser treated TiO2 photoanodes. Three different sets of experiments are conducted to identify the influences of laser treatment parameters.
1.The laser power density is fixed at 80mJ/cm2, and the number of laser irradiation pulses is varied as 0、2800、5600、11200、16800、22400 shots. The best cell efficiency is achieved with 11200 pulses of laser irradiation. The short-current density increased by ~13% and the conversion efficiency increased by ~24%.
2.The irradiation laser pulse number is fixed at 1000, and the power density is varied as 0、40、80、120、160、200 mJ/cm2. The best cell efficiency is obtained when the TiO2 photoanode is treated with a laser power density of 120 mJ/cm2, the short-current density increases by ~11% and conversion efficiency increases by ~20%.
3.The irradiation laser pulse number is fixed at 1, and the laser power density is varied as 0、40、80、120、160、200 mJ/cm2. No remarkable enhancement of short-current density and conversion efficiency is observed.
The dye-sensitized solar cells made with TiO2 photoanodes treated by multiple laser pulses show remarkable enhancement of short-circuit current, open-circuit voltage, fill factor and conversion efficiency. The rougher TiO2 surface morphology enhances the light scattering and light trapping, thereby improving the photocurrent levels and conversion efficiencies. Surface re-melting and solidification process also changes the surface status, reducing both the resistance of TiO2/dye/electrolyte interface and the TiO2 surface defect density. This leads to better fill factor and open circuit voltage. The open circuit voltage increases for DSSCs with photoanodes irradiated by only one laser pulse. However, in this case, the overall performance of solar cells is not improved. From the experimental results we can conclude that we need both appropriate laser power density and number of laser pulses to enhance the efficiency of DSSCs.