The photovoltaic performance of the heteroleptic H102 and HRD2 sensitizers was measured in DSSC and compared with that of reference N719 under similar fabrication and evaluation conditions. The Dye-Sensitised TiO2 electrodes were prepared by staining the electrodes in ethanol bath and 1/1 v/v acetonitrile/tert-butanol (binary liquid) mixture bath separately and the DSSCs based on these sensitizers show that the change of dye bath from ethanol to the binary liquid mixture enhances the photocurrent action spectrum and solar-to-electricity conversion efficiencies, (η). Using ethanol for sensitisation of TiO2 electrodes, the efficiencies obtained for H102, HRD2 and N719 are 4.31%, 4.62%, and 5.46%, respectively, while in binary liquid mixture bath, the corresponding values are enhanced to 5.89%, 4.87%, and 7.23%, respectively, under comparable conditions. 1. Introduction Among organic photovoltaic cells Dye-Sensitised Solar Cells (DSSCs) are known to be very promising due to their high efficiency and low-cost technology for the conversion of light energy into electricity [1–6]. The sensitizer is one of the most important elements that influence the overall performance of the DSSC. Ruthenium(II) polypyridyl complexes have wide applications as the most efficient sensitizers, because of the intense metal-to-ligand charge transfer (MLCT) transition exhibited in the visible region. Another important advantage of ruthenium sensitizers is their relative stability in oxidized and reduced forms and the ease of tuning their spectral, photo-physical, and electrochemical properties by bringing about structural changes in the bipyridyl ligand [7–13]. The most efficient test cell DSSC has been developed by Gr？tzel and coworkers by employing cis-dithiocyanato bis(4,4′-dicarboxy-2,2′-bipyridine)ruthenium(II) (known as N3 dye). The solar-to-electricity conversion efficiency up to 11% has been reached with N3 under AM 1.5？G on irradiation with a nanostructured TiO2 electrode and iodine redox electrolyte [14–17]. Usually anchoring ligands and ancillary ligands are incorporated in the metal-complex sensitizers so that anchoring ligands are responsible for grafting the dye on the semiconductor surface and providing a medium for electron injection from the excited state of the sensitizer to the conduction band of the semiconductor, whereas ancillary ligands have a scope for structural variations by chemical modifications for tuning the overall properties of the complexes. To ensure fast and efficient electron injection, one of the energy levels of the dye, lowest unoccupied
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