Experimental and Computational Studies on Bio-Inspired Flavylium Salts as Sensitizers for Dye-Sensitized Solar Cells

Abstract

Six new bio-inspired flavylium salts were synthesized and investigated by a combined computational and experimental study for dye-sensitized solar cell applications. The compounds were characterized by FT–IR, UV–Vis, NMR spectroscopy, and LC–MS spectrometry techniques. The pH-dependent photochromic properties of the flavylium dyes were investigated through a UV–Vis spectroscopy study and revealed that they follow the same network of chemical reactions as anthocyanins upon pH changes. The structural and electronic properties of the dyes were investigated using density functional theory (DFT) and time-dependent density functional theory (TD–DFT). Geometry optimization calculation revealed that all dyes, regardless of the specie, flavylium cations or quinoidal bases, present a planar geometry. The photovoltaic performances of the dyes, in both flavylium and quinoidal base forms, were evaluated by the HOMO and LUMO energies and by calculating the light-harvesting efficiencies, the free energy change of electron injection, and the free energy change regeneration. The MO analysis showed that all dyes can inject electrons into the conduction band of the TiO2 upon excitation and that the redox couple can regenerate the oxidized dyes. The results obtained for the free energy change of electron injection suggest that the quinoidal bases should inject electrons into the semiconductor more efficiently than the flavylium cations. The values for the free energy change regeneration showed that the redox electrolyte can easily regenerate all dyes. Dipole moment analysis was also performed. DSSCs based on the dyes, in both flavylium and quinoidal base forms, were assembled, and their photovoltaic performances were evaluated by measuring the open-circuit voltage, the short circuit current density, the fill factor, and the energy conversion efficiency. Results obtained by both experimental and computational studies showed that the overall performances of the DSSCs with the quinoidal forms were better than those obtained with the flavylium cations dyes.

Evaluation of Avocado Peels Dye as Sensitizer in Dye-Sensitized Solar Cells by Experiment and Computational Intelligence

“…It has already been established that perseorangin (PSG) and cyanidin (CND) are the key compounds in APPE responsible for colour [24,27]. While PSG typically should convey a yellow-orange colour, CND should convey a reddish-purple colour [27]. The structures of both PSG and CND were optimized and results are shown in Figure 5.…”

“…Results reveal that the E LUMO for PSG and CND are -2.62 eV and -0.33 eV respectively. The conduction band of TiO 2 has been experimentally determined to be -4.0 eV [27]. In other words, both PSG and CND have E LUMO values that are higher than the conduction band of TiO 2 as required for easy and effective injection of electrons from APPE and m-APPE into the TiO 2 conduction band.…”