Effect of solvent on dye-adsorption process and photovoltaic properties of dendritic organic dye on TiO_2 electrode of dye-sensitized solar cells

摘要

Correlation between the photovoltaic activity and adsorption characteristics of a TiO_2 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,l-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 TiO_2 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 TiO_2 surface. However, incomplete tethering of the Triple-PTZ dye molecules onto theTiO_2 surface substantially reduced the short-circuit current (J_(sc)). A good solvent promoted uniform adsorption of the Triple-PTZ dye on the TiO_2 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 TiO_2 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.