Replacing aromatic π-system with cycloalkyl in triphenylamine dyes to impact intramolecular charge transfer in dyes pertaining to dye-sensitized solar cells application

Abstract

In this study, five dyes comprising different donor moieties were proposed with a new design approach. In the triphenylamine (TPA) moiety, the lone pair electron on N takes part in resonance with three phenyl rings. As a result, the donating ability of TPA decreases in TPA-based dyes and hence the intramolecular charge transfer (ICT). We have proposed cycloalkyl moieties in place of phenyl moieties to stop the participation in the resonance of the lone pair with the other two phenyl rings so that the available lone pair on N will be pumped towards acceptor to achieve an efficient ICT. All dyes were subjected to density functional theory (DFT) and time-dependent DFT to evaluate their ground and excited-state properties. The projected density of state and natural bond orbital analyses were carried out to confirm the ICT from the donor to the acceptor moiety and also to comprehend the donating ability of the newly proposed donor moieties. The reorganization energy of the dyes was calculated to find out the conformational changes that occurred during photoexcitation. The dyes were attached to (1 0 1) anatase surface of TiO2 to understand the electron transfer from the excited-state of the dye to the conduction band of the TiO2. The adsorption energy of the dyes onto the (1 0 1) anatase surface of the TiO2 was also evaluated. The absence of defect states in the density of states spectrum indicated the smooth electron transfer at the dye/TiO2 interfaces.