Large Enhancement of Dye Sensitized Solar Cell Efficiency by Co-sensitizing Pyridyl- and Carboxylic Acid-Based Dyes

Co-sensitization is an attractive approach to enhance the light-harvesting efficiency of a dye sensitized solar cell (DSSC), whereby two or more dyes having complementary absorption spectra are co-adsorbed within a DSSC. A new method of co-sensitizing simultaneously pyridyl- and carboxylic acid-based dyes was performed and proved to be a successful approach for increasing the photoconversion efficiency (PCE%) of a DSSC. Yellow and red pyridyl-based dyes (T181 and T202) were co-sensitized with a blue carboxylic acid-based dye (Dyenamo Blue, DB). The co-sensitized DSSCs showed profound performance enhancements with a cobalt tris­(bipyridine) electrolyte system. Increases in the total cell efficiency of 45% and 16% were seen in the co-sensitized T181-DB and T202-DB cells when compared to the single dye-sensitized DB cell, respectively. Remarkable increases in photocurrent (<i>J</i>_sc) and photovoltage (<i>V</i>_oc) were seen in both co-sensitized cells. The higher <i>V</i>_oc values were mainly due to the decrease in the electron recombination processes at the TiO₂/cobalt electrolyte interface. The increase in dye coverage in the co-sensitized cells resulted in a blocking behavior at the TiO₂/electrolyte interface and had positive effects on electron lifetime. In addition the higher <i>J</i>_sc values were associated with the complementary absorption responses of T181 and T202 with DB as mirrored in the IPCE% spectra.