Two novel coumarin-substituted phthalocyanine dyes (CAPc and CSPc) with different linking units, using carboxylic groups as electron acceptor and injector, were designed, synthesized, and applied as panchromatic organic sensitizers in I−/I3−-based dye-sensitized solar cells (DSSCs). The asymmetric coumarin–phthalocyanine dyad analogue (OAPc) and the symmetric coumarin-phthalocyanine dyad analogue (COPc) were also synthesized for comparison. The structure–property relationship for these dyes was investigated by absorption spectroscopy, cyclic voltammetry, and thermogravimetric analysis. The ultraviolet–visible (UV–Vis) absorption was dramatically affected by the nature of the linker. Notably, modulation of the π-conjugated coumarin–phthalocyanine dyad CAPc and CSPc resulted in a large red-shift (Q-band above 710 nm); in particular, the dyad CAPc showed remarkably intense absorption in the spectral window of 450–650 nm. Electrochemical data for the dyes indicated that the azo double-bond-linked coumarin–phthalocyanine dyad dyes possessed relatively low-lying EHOMO values, which may be beneficial to suppress electron back-transfer from the conduction band of TiO2 to oxidized dyes due to facile regeneration of the oxidized dye by the electrolyte. Thermogravimetric analysis showed that the three coumarin–phthalocyanine dyad sensitizers were stable above 200 °C. When the dyads were applied as light-harvesting sensitizers in dye-sensitized solar cells, the cell sensitized by OAPc showed the best power conversion efficiency of 2.4%.

Two novel large conjugated system meso-Schiff-base substituted porphyrin dimers, which contained the thienyl or p-methylphenyl functional groups, have been designed and synthesized for the efficient green dyes for dye-sensitized solar cells (DSSCs) applications. The synthesis and characterization of the large conjugated system based on porphyrin dimer derivatives have been investigated through their spectral, electrochemical, and photovoltaic performances by DSSCs study. Due to the increase of the conjugated system, the two porphyrin dimers have some large red-shift at the maximum absorption, high fluorescence quantum yield. However, p-(10,15,20-triphenyl-5-porphyrinyl) benzylidene aminophenyl-10,15,20-(2-thienyl)-porphyrin, based on DSSCs reaching 2.86 % under AM 1.5 G irradiation, showed slightly better comprehensive properties than the p-(10,15,20-triphenyl-5-porphyrinyl) benzylidene aminophenyl-10,15, 20-(p-methylphenyl)-porphyrin.

Two donor–π-spacer–acceptor porphyrin dyes were synthesized for use in dye-sensitized solar cells. The dyes comprised the same donor (porphyrin derivative) consisting of 3,4,5-trimethoxybenzaldehyde and acceptor/anchoring group (carboxyl group) but varying π-spacer consisting of a Schiff base structure. Each of the dyes displayed different adsorption behavior and coverage on the TiO2 surface. The porphyrin dyes PZnBIACOOH studied in this work exhibit red-shifted and broadened electronic spectra respect to the reference PZnCOOH as expected. By the introduction of Schiff base unit at the meso positions, the energy level of Eox (excited-state oxidation potentials) is significantly shifted to the positive compared with the reference PZnCOOH, indicating a decreased HOMO–LUMO gap. The highest power conversion efficiency of the two dyes based on DSSCs reached 1.75% under AM 1.5 G irradiation.Graphical abstractMolecular structure of PZnCOOH and PZnBIACOOH.Highlights► Synthesis of two novel unsymmetrical zinc porphyrin sensitizers. ► Characterization of prepared compounds. ► Properties of novel zinc porphyrin sensitizers.