Photovoltaic performance of dye-sensitized solar cells stained with black dye under pressurized condition and mechanism for high efficiency

A porous TiO2 layer was stained with black dye (BD) under a pressurized CO2 atmosphere. Jsc of the cell (20.66 mA/cm2) was higher than that prepared by a conventional dipping process (18.96 mA/cm2). The higher Jsc was explained by the decrease in surface-state density on the nano-porous TiO2 layer. In addition, BD aggregation was found to be retarded under the pressurized CO2 condition, which is also associated with the higher Jsc. These phenomena were explained by the low BD concentration in the CO2 fluid, the swift reaction rate between TiOH and HOCO dye, and the high diffusion coefficient of BD molecules into porous TiO2 layers.