Photovoltaic properties of dye-sensitized solar cells associated with amphiphilic structure of ruthenium complex dyes

Abstract

Photovoltaic properties of Ru(2,2′-bipyridine-4,4′-bicarboxylic acid)(4,4′-bis(11-dodecenyl)-2,2′-bipyridine)(NCS)2 (denoted as Ru-C) related to its adsorption behavior onto the mesoporous titanium oxide (TiO2) were investigated in association with its amphiphilic structure compared with those of Ru(4,4′-dicarboxy-2,2′-bipyridine)2(NCS)2 (commonly known as N3 dye). Both dyes tended to aggregate and form vesicles in their acetonitrile/tert-butanol solutions. As the vesicles were adsorbed to TiO2, the dyes which did not participate in bonding to TiO2 would re-dissolve into the solution and create the voids on the surface of TiO2. The voids for N3 dyes would be filled in time, whereas a great deal of voids for Ru-C dye remained, presumably due to its aliphatic side chains retarding further adsorption. The dye sensitized solar cell (DSSC) using Ru-C dye has lower power conversion efficiency compared with N3 dye, which is partly due to the remaining voids that increase the charge recombination. Besides, the N3 dye that is capable of injecting the excited electrons from both ligands to TiO2 also enhances the photocurrent. Therefore, although using amphiphilic dye for DSSC may have a merit of long term stability, its tendency of void formation on TiO2 mesoporous layer needs to be concerned.