A Computational Prediction: Enhancing Visible Light Harvesting Through Minor Modification of Donor Moiety in Triphenylamine-Based Dyes for DSSCs

Five triphenylamine-based dyes were theoretically investigated using density functional theory (DFT) and time-dependent density functional theory (TDDFT) due to their structural configuration of (D–π–A) which has potential applications as sensitizers for dye-sensitized solar cells (DSSCs). One dye was sourced from the literature, (E)-2-cyano-3-(5-(6-(diphenylamino)-3,3-dimethyl-3H-indol-2-yl)thiophen-2-yl)acrylic acid, denoted as (I), and the remaining dyes (from II to V) are inspired by the former with minor structural change in the indole moiety of donor part. These molecular structures are composed of different diphenyl indole amine species (donor part), thiophene (π-bridge), and cyanoacrylic acid (acceptor part). This study focused on the effect of small structural change in the five-membered ring of the indole moiety on the geometric, electronic, and optical properties of the studied dyes as well as their potential applications as sensitizers for DSSCs. Due to this structural change, a twist in the molecular skeleton of the designed dyes was observed, resulting in a new band at a longer wavelength that spans the visible region. This band is attributed to the phenomenon of twisting intramolecular charge transfer (TICT). The findings reveal that the minor structural change in the indole moiety enhanced the harvesting character of designed dyes that makes them promising candidates for application in DSSCs.