Zn(II)-porphyrin dyes with several electron acceptor groups linked by vinyl-fluorene or vinyl-thiophene spacers for dye-sensitized solar cells

• New porphyrin-based molecules for solar energy conversion.
• Highest efficiency of 5.56%.
• Changing thiophene to fluorene significantly reduces the observed efficiencies.

Herein we report the design, synthesis, and characterization of a series of new organic dyes, as well as their application in dye-sensitized nanocrystalline TiO2 solar cells. In the designed dyes, the diphenylamine Zn(II) porphyrin group plays the role of the core electron donor unit and the cyanoacrylic acid, rhodanine acetic acid, and dicyanorhodanine groups are the acceptors. These electroactive units are linked by either vinyl-fluorene or vinyl-thiophene spacer units. To study the electron distribution and the intramolecular charge transfer the HOMO-LUMO levels of the dyes were calculated by computational methods and experimentally using electrochemical measurements. The DSSCs based on the dyes bearing a cyanoacrylic acid acceptor group showed the best photovoltaic performance with short-circuit photocurrent densities of 12.66 and 13.58 mA/cm2, open-circuit photovoltages of 0.675 and 0.651 V, and fill factors of 0.628 and 0.441, corresponding to an overall conversion efficiency of 5.56 and 4.13%, respectively, under AM 1.5 irradiation (100 mW/cm2).

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