A quantum chemistry study on the performance of porphyrin-based solar cell sensitisers; Zinc and anchor group position effects

In this work, ten porphyrin derivatives, including free-base zinc-metalised compounds were studied by varying the position of the carboxyl anchoring group and the alkyl substituents length on the remaining three phenyl rings with the aim of the cell efficiency investigation. Theoretical performances of the sensitisers in the dye-sensitised solar cell systems have been discussed by analysis of the optical absorption, the oxidised potential of ground and excited states, light-harvesting efficiency and electron injection efficiency. Due to lower symmetry of free-based porphyrins, they showed broader bands than zinc porphyrins. The second group sensitisers are better than the first one due to the smaller oxidation potential energy, higher open-circuit voltage and light-harvesting efficiency. The influence of long alkyl substituents on the photovoltaic parameters is not perceptible but ortho and meta positions of anchoring group modify the solar cell performance. Finally, some correlations between the quantum reactivity indices and photovoltaic parameters have obtained and discussed.