Effects of paste storage on the properties of nanostructured thin films for the development of dye-sensitized solar cells

The effects of paste storage on the properties of nanostructured thin films were investigated in the present study. To this aim, dye-sensitized solar cells were fabricated using nanostructured TiO2 thin films and an organic dye as a sensitizer. Aggregation of TiO2 nanoparticles was observed when paste was stored until deposition affecting film's porosity and surface roughness factor and as a consequence, reducing the efficiency of the solar cells. On the other hand, fewer cracks were developed during the drying process of the film when stored paste was used for film deposition instead of freshly prepared paste. This is due to the presence of large pores on films with significant particle agglomeration, which enhance evaporation of acetyl acetone and water, thereby reducing cracks. The development of cracks on the film's surface results to a decrease in the efficiency of the cell, albeit a slight one. One of the main aims of the present study was also the investigation of different methods for developing counter electrodes, as the properties of the counter electrodes can affect the efficiency of the solar cells considerably. Counter electrodes were prepared by two different methods, namely by electrodeposition using an aqueous solution of H2PtCl6 (0.002 M) and by thermal decomposition of H2PtCl6 from isopropanol (5 mM). Electrodeposited counter electrodes were found to present several advantages over electrodes prepared by thermal decomposition, such as increased photocurrent, reduced sheet resistance, as well improved fill factor for the resulting solar cell.