A click-chemistry approach for the synthesis of porphyrin dyads as sensitizers for dye-sensitized solar cells

Two novel porphyrin dyads (9 and 11) consisting of two zinc-metallated porphyrin units, covalently linked at their peripheries through 1,2,3-triazole containing bridges and functionalized by a terminal carboxylic acid group, have been synthesized via click reactions, which are Cu-catalyzed Huisgen 1,3-dipolar cycloadditions between azide-and acetylene-containing porphyrins. Photophysical and electrochemical measurements, together with DFT calculations, showed that the two dyads possess suitable frontier orbital energy levels for use as sensitizers in DSSCs. The 9 and 11 based solar cells were fabricated resulting in power conversion efficiencies (PCEs) of 3.82 and 5.16%, respectively. 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 latter is attributed to its enhanced photovoltaic parameters, and particularly its enhanced short circuit current (J(sc)). This is related to the stronger absorption profile of the sensitizing dyad 11 (the dyad with the shorter triazole containing bridge) and the higher dye loading of the corresponding solar cell. Furthermore, electrochemical impedance spectra (EIS) demonstrated that the 11 based solar cell exhibits longer electron lifetime (tau(e)) and more effective suppression of the recombination between the injected electrons and the electrolyte.