Theoretical design of new triphenylamine based dyes for the fabrication of DSSCs: A DFT/TD-DFT study

A series of rigid triphenylamine (TPA) dyes have been designed with the donor(D)-pi-acceptor(A) architecture. The rigid TPA unit is designed by locking the two phenyl rings with alkyl and ethylene chain to attain better planarity and to minimize its rotation. Four different acceptor units viz. BTz, BBTz, PzT and PyT are used to design four parent dye systems. The study reveals that all four dyes show low Delta(H-L) values whereas only BTz, PyT and PzT dyes show small dihedral angles. Moreover, excited state calculation of these three dyes show excellent electronic transition properties with a sharp absorption (lambda(max)) in the range of 507-540 nm at the UV-vis spectra. The lambda(max) values of BTz, PyT and PzT dyes show a red shift to that of the reference dye which signifies better electronic transition from HOMO to LUMO orbitals. It is further supported by the MO diagrams of the dyes where the MOs of BBTz dye shows less overlap between the occupied and unoccupied orbitals. It is also evident from the low EA and IP values that the three dye systems (excluding BBTz) should show excellent transfer of injected electron to the semiconducting surface. Low lambda(+) and high k(CT)(+) values imply the hole transporting nature of the designed dyes. Hence, these dyes will act as potential candidates for fabrication of dye-sensitized solar cells (DSSCs).