Impact of internal (donor/acceptor) moieties and π-spacer in triphenylamine-based dyes for DSSCs

The impact of internal (donor/acceptor) groups and π-spacers (benzene/thiophene) are investigated in dye-sensitized solar cells (DSSCs) using a series of D-A-π-A and D-D-π-A type organic dyes. These dyes have a triphenylamine donor, different internal acceptor (A) or donor (D) groups and thiophene/benzene as a π-spacer combined with an acceptor cyanoacrylic acid. Density functional theory (DFT) and time-dependent DFT (TDDFT) approaches were used to investigate the dye geometries, as well as electronic excitations and charge transport characteristics. The frontier molecular orbital energies and energy gaps facilitated for the consideration of appropriate energy levels for dye regeneration, electron transfer and electron injection. The short circuit current density (JSC) calculations were achieved by using dye regeneration energy (ΔGreg), injection driving force (ΔGinj) and light harvesting efficiency (LHE). Charge transport properties like electron affinities (EA), ionization potentials (IP), along with reorganization energies (λh and λe) are also described. The outcomes show that adding an internal donor/acceptor in D-π-A arrangement and different π-bridge influences the absorption energies and enhanced photovoltaic characteristics. As a result, the fundamental goal of this research is to establish a theoretical foundation for appropriate structural changes and design in the development of efficient DSSCs.