Photophysical, electrochemical and photovoltaic properties of dye sensitized solar cells using a series of pyridyl functionalized porphyrin dyes

Three porphyrin dyes, P1, P2 and P3, bearing one, two and four pyridyl groups, respectively, in the meso positions, acting as electron acceptor anchoring groups, were synthesized, characterized and investigated as sensitizers for the fabrication of dye sensitized solar cells (DSSCs). The overall power conversion efficiencies (PCEs) of DSSCs based on these dyes lay in the range 2.46-3.9% using a 12 mu m thick TiO2 photoanode. Porphyrin P2 achieved the maximum performance, which can be rationalized by the high dye loading, efficient electron injection, dye regeneration process and longer electron lifetime, as demonstrated by the electrochemical impedance spectroscopy (EIS) measurements. The PCE of the DSSC based on the P2 sensitizer when the photoanode was treated with formic acid, showed an enhanced efficiency of 5.23%. This improvement, attributed to multifunctional properties such as higher dye uptake, reduced recombination process and enhanced charge collection efficiency. Deoxycholic acid (DCA) was also used as a coadsorbent in order to prevent dye aggregation and it was found that the PCE improved up to 6.12% for sensitizer P2 and the modified TiO2 photoanode, which can be attributed to further improvement in the electron injection efficiency and charge collection efficiency.