A new family of A 2B 2 type porphyrin derivatives: Synthesis, physicochemical characterization and their application in dye-sensitized solar cells

Abstract

A new series of A 2B 2 type porphyrins, i.e. free base P1 and Zn-complex P2, have been synthesized and characterized as photosensitizers for dye sensitized solar cells (DSSCs). These dye molecules contain a porphyrin unit as a π-spacer, two N,N′-dimethylphenyl groups as electron donors and two phenylcarboxylic acid moieties as anchoring groups yielding push push-pull pull type porphyrins. The photophysical as well as electrochemical properties of the two dyes (P1 and P2) were investigated by UV-Vis, fluorescence spectroscopy and cyclic voltammetry. The DFT results showed that the HOMO is located on the donor group and the LUMO is located on the anchoring carboxylate group indicating their suitability for fabrication in DSSCs. Under photovoltaic measurements, overall PCEs of 3.80% and 4.90% were achieved with the DSSCs based on P1 and P2 dyes, respectively. The overall PCEs have been further improved up to 4.83% and 6.07%, with P1 and P2 dyes when CDCA co-adsorbent was added to the dye solution. The electrochemical impedance data indicate that the electron lifetime was improved by the coadsorption of CDCA, which was attributed to the improvement in both V oc and J sc. The increase in J sc has also been attributed to the reduction of the back reaction, i.e. the recombination of electrons with tri-iodide ions. © 2012 The Royal Society of Chemistry.