A supramolecular assembling of zinc porphyrin with a π-conjugated oligo(phenylenevinylene) (oPPV) molecular wire for dye sensitized solar cell

Abstract

A novel π-conjugated oligo(phenylenevinylene) (oPPV) (or LC) was prepared, as a new organic dye for dye-sensitized solar cells (DSSC), which contains a cyanoacrylic acid group on one end and a pyridyl group on the other. Solar cells sensitized by LC were fabricated, and were found to exhibit a power conversion efficiency (PCE) value of 2.45%. Furthermore, we describe the formation of a supramolecular dyad (ZnTPP–LC) via a metal–ligand bond between LC, since its pyridyl group allows it to interact with several metal centers, and zinc-tetraphenyl-porphyrin (ZnTPP) onto the photoelectrode's TiO₂ surface of the solar cell. More specifically, LC was bound at first onto TiO₂ with its cyanoacrylic acid anchoring group, and then a metal–ligand supramolecular bond was formed, with the addition of a porphyrinic solution, between the nitrogen atom of LC's pyridyl group and the zinc. ZnTPP–LC solar cell was then fabricated resulting in a record PCE value of 5.27% concerning the supramolecular DSSCs. As shown by photovoltaic measurements (J–V curves) and incident photon to current conversion efficiency (IPCE) spectra of the two solar cells, the higher PCE value of the supramolecular one can be attributed to its enhanced photovoltaic parameters, and particularly its enhanced short circuit current (J_sc). This J_sc improvement is due to ZnTPP–LC's higher light-harvesting efficiency and the larger electron injection of both ZnTPP and LC into TiO₂'s conduction band (CB) of the corresponding solar cell. These results are in accordance with electrochemical impedance spectra (EIS) of the DSSCs, which revealed longer electron lifetime, higher charge recombination resistance and shorter electron transport time for the solar cell based on ZnTPP–LC as compared to the one sensitized by LC.