Extracts from Capsicum annuum as Natural sensitizer in Dye Sensitized Solar Cell : Theoretical analysis using DFT and TD-DFT

Abstract

Sensitizers derived from Capsicum annum were studied using computational methods (DFT and TD-DFT) for their potential application in DSSC. The UV-Vis computed spectra describe a band around 450 nm that involves a π-π* electronic transition associated with the frontier orbitals HOMO -LUMO localized in the large chain of double bonds of the capsorubin and capsanthin. This very much coincides with the experimental values and shows a potential activity for the photoexcitation. Moreover, the behaviour towards the adsorption and electron injection of the Capsicum annuum to TiO2 semiconductor was analyzed through periodic calculations of the capsorubin@(TiO2)72, capsanthin@(TiO2)72 and capsaicin@(TiO2)72 models. The first two show an opposite result for the capsaicin sensitizer. Specifically, hydrogen bonds were found between the methyl substituents of the carotenoids and the oxygen on the TiO2 surface, suggesting an O-H electrostatic interaction. Capsaicin was found to lose linearity around the amide group (C-NH-CO 180°), transforming into an angular rearrangement (C-NH-CO 120°). These structural changes influence the electronic injection of Capsicum annuum into the TiO2 semiconductor. Thus, the low efficiency reported in carotenoid is due to the presence of weak interactions.