New pyridyl-based dyes for co-sensitization in dye sensitized solar cells

Abstract

Co-sensitization is very advantageous in increasing a dye sensitized solar cell’s (DSSC) efficiency. It relies on sensitizing the same titania film with two dyes that have complementary absorption spectra. In this report we describe co-sensitization of dyes with pyridine anchoring groups with carboxylic-acid based ones having complementary absorption spectra. Six new pyridine based dyes with colors ranging from yellow to turquoise have been synthesized and characterized. T220, a yellow dye, was co-sensitized with Dyenamo Blue, a commercially available blue dye. This approach showed good performance enhancement compared to individual dye sensitized cells with a Co(II/III) redox mediator. An increase in the photocurrent (JSC), photo-voltage (Voc) and thus total efficiency (PCE%) were seen. The close packing of the two dyes in the co-sensitized devise caused a decrease in the electron recombination processes at the TiO2/electrolyte interface, thus resulting in higher Voc values. Such an increase in dye coverage results in a blocking behavior at the TiO2/electrolyte interface, as mirrored in the performed electrochemical impedance spectroscopy (EIS) experiments, where higher charge recombination resistance (RCT) and longer electron lifetime were measured in the co-sensitized DSSCs.