Synthesis, Optical and Photovoltaic Properties of Porphyrin Dyes

The synthesis and optical absorption of a series of porphyrins, and the photoelectrochemical properties of TiO2 solar cells sensititized with these porphyrins was investigated. The different types of porphyrins studied are designated by numbers: the reference compound 1 (Zinc(II) 5,15-bis(4-carboxylphenyl)porphyrin), porphyrin substituted with one triarylamine unit 2, and porphyrin substituted with two triarylamine units 3. The UV-Vis absorption spectra reveal that the substitutions result in large redshifts in both the Soret band ( 60 nm) and the Q bands ( 125 nm), as well as enhancement of optical absorption. The enhancement is even more pronounced in the long-wavelength region of 575-725 nm, where the absorption of porphyrin 3 is eight times that of porphyrin 1. The photoelectrochemical properties of the porphyrins were also studied by constructing porphyrin-sensitized TiO2 solar cells. Under standard AM 1.5 sunlight, the porphyrin 1 cell yields a short-circuit current of 1.26 mA/cm2, an open-circuit voltage of 0.564 V, and a fill factor of 61%. The incident photon-to-current conversion efficiency is 24% for porphyrin 1 and 5-7% for porphyrins 2 and 3 at the Soret peak.