Phenothiazine dyes bearing fluorenone unit for dye-sensitized solar cells

Abstract

Three N-phenylphenothiazine dyes were synthesized with fluorenone linked with aryl rings as π-bridges and cyanoacrylic acid as the electron acceptor. Their photophysical properties, electrochemical properties and photovoltaic performance were evaluated. Dyes with furan and thiophene bridges show longer ICT absorption wavelength and display distinctly broader and higher light absorption range on TiO2 film. Dye with benzene bridge has an inferior molecular planarity due to the larger dihedral angle between the fluorenone unit and benzene ring, which blueshifts its ICT absorption but favors its antiaggregation. Thus, dye with thiophene bridge achieves the highest JSC while dye with benzene bridge achieves the highest VOC. However, DSSC based on dye with furan bridge obtains the optimal photoelectric conversion efficiency due to better JSC and VOC and the highest ff. Compared with their carbazole counterpart, these phenothiazine dyes show the improved JSC and VOC, therefore, achieve higher photovoltaic conversion efficiency.