Synthesis of new macrocyclic sensitizers for photoelectrochemical devices

Gloria Zanotti, Nicola Angelini, Sara Notarantonio, Anna Maria Paoletti, Giovanna Pennesi, Gentilina Rossi

Dye-sensitized solar cells were developed by the Swiss chemist Michael Grätzel in 1991 and are also known as “Grätzel cells”. They are electrochemical multicomponent “sandwich-type” devices which are a promising alternative to the conventional silicon-based cells, because of their lower costs of production and of the significant improvements in the fields of molecular electronics and nanotechnology, which have allowed to push the efficiency values of these devices from an original 7% in 1991 up to 13%. In a Dye Sensitized Solar Cell, sunlight passes through the transparent electrode into the dye layer where it can generate charges that then flow into the titanium dioxide. After flowing through the external circuit, they are re-introduced into the cell on a metal electrode on the back, flowing into the electrolyte. The electrolyte then transports the electrons back to the dye molecules. Many kind of dyes are used in DSSC including molecules that are similar to the natural photosyntetic pigments like Chlorophilla.


Among these kind of dyes, porphyrins, benzoporphyrins, phthalocyanines have been applied to the light harvesting process related to organic photovoltaics, with particular focus on polymer cells and Dye-Sensitized Solar Cells.





We have synthesized up to now several phthalocyanine dyes (1,2) and we are now investigating the behaviour of macrocyclic compounds having a structure that could potentially combine the best features of these molecules and we’ve specifically focused our attention on benzoporphyrins. Their main goal is obtaining an hybrid Pc/Ph aromatic structure with an intense absorption in the visible and rear-IR regions of the solar spectrum that can be modulated by an accurate tailoring of their periphery and have never been extensively studied as chromophores in DSSC devices. The molecule we’ve synthesized (3) shows an intense and brilliant green colour and has given an efficiency of 2,15% when tested in a DSSC device.


(3) structure of target benzoporphyrin




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