A computational study on boron dipyromethene ancillary acceptor-based dyes for dye-sensitized solar cells

Abstract
A series of (D-π)2-An-A based organic dyes containing boron dipyrromethene (BODIPY) moiety as an ancillary acceptor (An) derivative were chosen, and the effect of donor moieties
(diarylamine, carbazole, azepine, and dibenzazepine) was investigated to understand their photophysical and photoelectrochemical properties by employing density functional theory (DFT) and time-dependent DFT. It is experimentally proved that BODIPY enhances the
light-harvesting in red and near IR region of visible light. The electron density distribution analysis was performed for all the dyes to confirm the intramolecular charge transfer,
envisioned from the simulated absorption spectra of the dyes. Carbazole donor-based dye exhibited the lowest reorganization energy. A dye attached to the TiO2 (1 0 1) surface was
modeled to estimate the adsorption energy of the dyes. The density of states analysis revealed that the absence of defect states in the bandgap of TiO2 facilitates the smooth electron
transfer from the excited state of the dye to the conduction band of TiO2. Considering the lowest unoccupied molecular orbital (LUMO) energy level of dyes and conduction band energy level of TiO2, it is understood that all the dyes studied in this study are capable of electron injection upon photoexcitation. Considering the driving force for dye regeneration of
Page 1 of 30 New Journal of Chemistry New Journal of Chemistry Accepted Manuscript Published on 20 February 2020. Downloaded on 2/26/2020 2:51:59 AM. View Article Online DOI: 10.1039/C9NJ05334D the dyes and the magnitude of reorganization energy, carbazole donor-based dye (D2) would
be the best performing dye in DSSC. Previously, the power conversion efficiencies of the dyes have been reported, and carbazole donor-based dye (D2) exhibited the highest efficiency
among all the dyes. Our computational investigations are in good agreement with the experimental results.