Energy levels for DSSC based in phycocyanin as natural dye

MARÍA FERNANDA CERDÁ; PAULA ENCISO; FRANCO M. CABRERIZO

Lausanne

Congreso; 65th Annual Meeting of the International Society of Electrochemistry; 2014

Phycocyanin, a blue protein extracted from Spirulina spp, shows promising characteristics that made it suitable for its use as natural dye in photovoltaic devices such as dye sensitized solar cells. In this work, a study of the aqueous solution-phase photochemistry, photophysics, spectroscopy and voltammetry is presented. Suitable redox potentials (Eox = 1.2 V vs. SHE) and a value of 1.96 V for E0,0 (i.e., the energy difference between the vibrationally relaxed levels of the first electronic excited state, S1, and the ground state, S0 of phycocyanin), allows the calculation of energetic profiles that in comparison with the conduction band of the anatase-TiO2 and I-/I3- electrolyte, could predict electron transfer with this components of the cell. Phycocyanin was extracted from commercial capsules of Spirulina spp. UV-vis and fluorescence measurements were recorded. Cyclic voltammetry was performed using an Au-pc working electrode, a Ag/AgCl as reference and graphite as counter electrode. UV-visible spectrum of phycocyanin in aqueous solution showed the presence of two maxima centered at 410 and 619 nm. Fluorescence emission spectrum shows an intersection with the excitation spectrum at 634 nm, and as a consequence, E0,0 value was calculated as1.96 eV. Cyclic voltammetric profiles showed adsorption through the carboxylic groups of phycocyanin to gold. An anodic contribution is observed at 1.2 V, with the counter peak at ca. 0.3 V. Considering also the E0,0 value of 1.96 eV, the Rehm-Weller equation can be applied, arising an oxidation potential for the excited state of the phycocyanin of -0.76 V. According to this and also taking a 0.53 V value for the conduction potential of TiO2, it is possible to predict a spontaneous process of electron transference between the blue protein and the TiO2. On the other hand, if a value of 0.35 V for I-/I3- is also considered, the regeneration of the oxidized dye on the counter electrode surface would also take place. The first step, involves the oxidation of the dye as a consequence of the incident light followed for an electron transfer from the excited dye to the semiconductor, and certainly allows the switch on of the cell. The cycle will be completed by the last step that involves the regeneration of the dye due to the iodine species. These will allow reusing the dye in later cycles.