Effect of solvent on dye-adsorption process and photovoltaic properties of dendritic organic dye on TiO₂ electrode of dye-sensitized solar cells

Correlation between the photovoltaic activity and adsorption characteristics of a TiO₂ electrode coated with an organo-dendritic dye containing three chromophores in one molecule ((2E,2′E,2″E)-3, 3′,3″-(10,10′,10″-(6,6′,6″-(4,4′, 4″-(ethane-1,1,1-triyl)tris(benzene-4,1-diyl))tris (oxy)tris(hexane-6,1- diyl))tris(10H-phenothiazine-10,3-diyl))tris(2-cyanoacrylic acid), triple-PTZ) was investigated by applying it in dye-sensitized solar cells (DSSCs). The photovoltaic performance of the DSSCs utilizing the Triple-PTZ dyes varied based on the solvent conditions employed for adsorbing the dye on the TiO₂ electrode surface. Aggregation of the Triple-PTZ dyes on the electrode surface was induced in the poor solvent system, with a consequent increase in the total amount of Triple-PTZ dye, which is directly adsorbed on the TiO₂ surface. However, incomplete tethering of the Triple-PTZ dye molecules onto the TiO₂ surface substantially reduced the short-circuit current (J _sc). A good solvent promoted uniform adsorption of the Triple-PTZ dye on the TiO₂ surface, with a consequent enhancement of the power conversion efficiency (PCE) of the fabricated DSSCs up to 4.90%, which is much higher than the PCE of 1.93% obtained from the DSSC fabricated using the poor solvent system. The correlation between the adsorption properties of the photosensitizing Triple-PTZ dyes on the TiO₂ electrode and the photovoltaic performance was intensively investigated with the help of ATR-FT-IR spectroscopy, the incident photon-to-electron conversion efficiency (IPCE), and electrochemical impedance spectroscopy (EIS) analysis.