The study of the condensed matter, and the mechanisms that govern the behaviors of their constituting molecules is a fascinating topic. The curiosity to discover their properties stimulates the creativeness of the researchers that look it in order to exploit knowledges both for mere scientific aims and for their applications. These efforts are contributing to widen the cultural patrimony of the society and its general development.
Solar cells: Unlike to silicon cells, known as photovoltaics, the solar cells are photoelectrochemical devices having the same goal; the convertion of the light coming from the sun in electric energy. Solar cells use a dye (cromoforo) whose electrons, excited by the light, are at the first transfered on titanium oxide nanocrystals and then towards the negative electrode (anode).
An appropriate redox couple (Iodide/Iodine) provides electrons, coming from cathode, inorder to oxidized the dye. In this manner, the electric circuit is closed by electron flux. In other words the sun is the pump able to mantein the device activity. This process is very similar to the chlorophyllian photosintesis.
The solar energy conversion efficiency (n) of these devices is of the order of 10%. This value is inferior to that attainable with the standard silicon cell (16%). Nevertheless, the solar cells have a better termic stability with a constant efficiency, also in critical illumination conditions.
Dyes: althought, organics and inorganics synthetic compounds are usually employed, an available alternative is furnished by natural anthocyans, the molecules that give the colour to the vegetables ( fruits, flawers, etc.). In particular utilized red Sicilian orange, eggplant peels, blackberry, grapes have been utilized : natural dyes are abundant, non toxic, biocompatible, and totally recyclabe
Counterelectrode: alternative material to the platinum cathode, usually employed also as catalyst, are furnisched by carbon nanotubes, graphite, black smoke and so on.
Cell preparation: the realization of such a photo-electrochemical device is simpler, more economic and to lower environmental impact in comparison to the actual silicon cells. A thin film of titanium oxide nanoparticles (thickness around 12 microns) is deposited on a glass transparent conductor which is soakesand in a dye solution. Such electrode (anode), is further treated with electrolitic solution and covered with the cathode to form the galvanic cell which can be turned into electrolitic cell.
This last, forces the electrons to flow in opposite sense in respect to the former, converting electric energy in chemical energy (production of metals, gas, etc.)
Photoelectrochemical properties of natural dyes solar cells under A. M. 1.5 and 100 mW/m2, considered paramiters (Jsc(mA/cm2), Voc(mV), Jmax(mA/cm2), Vmax(mV), F.F.(%), n(%)): extract of eggplant Skin (Solanum Melongena) 3.40, 350, 2.413, 200, 40, 0.48, juice of red orange (Citrus Sinensis) 3.84, 340, 2.92 , 225, 50, 0.66, red wine (Vitis Vinifera) 2.35, 300, 1.59 , 150, 33, 0.24, cis-(dcbH2)2Ru(NCS)2 10.94, 660, 10.00, 450, 62, 4.5.
La natura non opera con l'intervento di molte cose quel che si può fare con il mezzo di poche...(Galileo. Dialogo dei massimi sistemi, Giornata seconda).
Immagini:
