Influence of the number of phenylethynyl units present in porphyrin sensitizer on its light harvesting and cell performance

Four phenylethynyl-porphyrins 4a , 4b , 5a , and 5b with either one ( 4a and 4b ) or two ( 5a and 5b ) phenylethynyl groups attached at C10 or/and C20 position of the porphyrin ring (defined as the axial direction), and with phenyl ( 4a and 5a ) or 2,6-dialkoxylphenyl group ( 4b and 5b ) at C5 position of porphyrin in a push–pull framework (defined as the push–pull direction) were designed and synthesized. The synthesized porphyrins were applied in dye-sensitized solar cells (DSSCs). Unexpectedly, although the light harvesting capability of the dye is enhanced with the increase of the number of phenylethynyl group as indicated in the UV–Vis spectra, the light to electricity conversion efficiency ( η ) of the corresponding solar cell drops. The influence of the number of the phenylethynyl group present along the axial direction of the porphyrin on the photovoltaic performance of DSSCs is well explained by the condensed Fukui function obtained via DFT calculations.