Combination of natural betanidin dye with synthetic organic sensitiser towards dye-sensitised solar cell application

Abstract

Betanidins belong to natural red-purple pigments betacyanins, which experimentally demonstrated good light adsorption in a visible range and might be suitable for the dye sensitised solar cell (DSSCs). Instability is a well-known drawback of natural dyes, which impedes their use for DSSCs. A thermodynamic approach helps to understand the betanidin (Bd) instability which occurs due to spontaneous decarboxylation reaction with decarboxylated betanidin (dBd) formation. The study considers the improvement of the sensitiser’s functionality via combination of natural Bd/dBd dyes and synthetic 4- (Diphenylamino)phenylcyanoacrylic acid (L0) dye. Novel complex D–π–A organic dyes, L0–Bd and L0–dBd with structural isomers, have been designed via esterification reactions. The DFT/B3LYP5/6‒31G(d,p) approach has been used to compute geometry, vibrational spectra and thermodynamic characteristics of the individual isomers and their complexes with L0. Implementation of TD–DFT method aids in obtaining optoelectronic properties. The broader coverage of the solar spectrum with greater light-harvesting efficiency was achieved for the complexes compared to individual dyes. The dyes attachment to the semiconductor TiO2 was simulated in terms of different adsorption modes to hydrogenated (TiO2)6 cluster. Binding energies and electronic spectra of the dye@TiO2 systems were computed, and electron density distributions over frontier molecular orbitals analysed. Binding energy magnitudes varied within 15‒21 eV for the dye@TiO2 systems.