Porphyrins modified with a low-band-gap chromophore for dye-sensitized solar cells

Abstract

Two novel porphyrin dyes (PMBTZ and PHBTZ) modified with alkyl-thiophene and 2,1,3-benzothiadiazole (BTZ) moieties were designed and synthesized. The optical and electrochemical properties were characterized by UV–visible, fluorescence spectroscopy and cyclic voltammetry. With the introduction of the low-band-gap chromophore onto the porphyrins, the absorption spectra of the two porphyrin dyes in the range of 450–600nm were broadened and the maximum wavelength was red-shifted compared with PZn as expected. The first oxidation potentials (Eox1) were altered to the negative, which lowered from 1.27 to 1.11 and 1.15eV, respectively. For a typical solar cell device based on dye PMBTZ, the maximal monochromatic incident photon-to-current conversion efficiency (IPCE) can reach to 65%, with a broad respondent region of 350–800nm. Under standard global AM 1.5 solar condition, the dye-sensitized solar cell (DSSC) based on the dye PMBTZ showed the best photovoltaic performance: a short-circuit photocurrent density (Jsc) of 14.11mA/cm2, an open-circuit photo voltage (Voc) of 0.59V, and a fill factor (ff) of 0.66, corresponding to solar-to-electric power conversion efficiency (η) of 5.46%.