DFT, DFTB and TD-DFT theoretical investigations of π-conjugated molecules based on thieno[2,3-b] indole for dye-sensitized solar cell applications

Abstract

In this study, the electrochemical, photovoltaic and absorption properties of the new designed organic sensitizers dyes: Dye-1, Dye-2, Dye-3 and Dye-4 based on Dye-R, of D-π-A architecture, before and after binding to the TiO2 cluster surface on the ability to inject electrons to the surface. The D donor is the thieno[2,3-b] indole, π-spacer is thiophene, A acceptor is cycnoacrylic acid (CA). The properties were calculated using functional density theory (DFT), time-dependent TD-DFT and the density-functional tight-binding (DFTB) approach. Our study also focused on the analysis of the effects of the introduction of the auxiliary donor (D′)/acceptor (A′) groups on the main photovoltaic properties of the reference molecule Dye-R and to study the relationship between the molecular structure and optoelectronic properties. The analysis of the calculated properties of the new designed compounds D-D′-π-A (Dye-1), D-π-D′-A (Dye-2), D-A′-π-A (Dye-3) and D-π-A′-A (Dye-4), where A′ is benzothiadiazole and D′ is 9,9-diethyl-9H-fluorene, indicate that the molecular architecture has a significant effect on various properties of the studied dyes and that nature (donor D ′or acceptor A′) of the introduced groups, as well as the choice of their locations with respect to the π bridge, is of great importance. Indeed, among the four designed compounds Dye-4 (D-π-A′-A) and Dye-3 (D-A′-π-A) display significantly better properties than those of the reference molecule Dye-R (D-π-A) and of the two other designed dyes Dye-1 (D-D′-π-A), Dye-2 (D-π-D′-A).