A computational investigation of the influence of acceptor moieties on photovoltaic performances and adsorption onto the TiO<inf>2</inf> surface in triphenylamine-based dyes for DSSC application

Five metal-free organic dyes (A1 to A5) comprising triphenylamine and vinyl-thiophene as a common donor and spacer, respectively were considered in this work. The different acceptors, such as 2-cyanoacetic acid, 2-methylenemalononitrile, rhodanine-3-acetic acid, benzoic acid, and pyridine were chosen to investigate their accepting ability, photovoltaic performances, and adsorption onto the TiO2 surface. Density functional theory (DFT) and time-dependent DFT were employed to study their photophysical and photoelectrochemical properties. The ground state energies were calculated to evaluate the dye regeneration driving force (EI3-/I--EHOMO). The excited-state calculation provided the information about the intramolecular charge transfer (ICT) and excited-state properties. Projected density of state and natural bond orbital (NBO) analyses were carried out to further understand the ICT between triphenylamine donor and the acceptor moiety. The density of states of the dye@TiO2 revealed the smooth electron transfer at the dye/TiO2 interface devoid of defect state. Higher (EI3-/I--EHOMO), highest negative NBO charge on the acceptor, lower reorganization energy, and higher negative adsorption energy onto the surface of the TiO2 would make the dye A1 as the best performer in DSSC. The computed data are in good agreement with the experimental observation.