DFT and TD-DFT optoelectronic study on hybrid alizarin-carbazol based dyes incorporated on titanium dioxide (TiO2) for dye sensitized solar cell application

The optical, electronic and structural properties of six hybrid alizarin-carbazol based dyes with different pi-spacers before and after binding to a TiO2 were studied in detail by using DFT and TD-DFT calculations to understand their application in dye-sensitized solar cells (DSSCs). On the basis of the isolated dyes, energy levels, frontier molecular orbitals, optical properties, and the interactions of dyes and TiO2 semiconductors were investigated. Our results show that the photophysical and photo-electrochemical properties of designed dyes were improved by introduction of electron-rich heterocyclic rings as a pi-spacer moiety, which led to a reduction in the designed dyes band gap and as a result of light absorption spectra red-shifting and the DSSCs energy conversion efficiency. This study is expected to give perspectives for future developments and optimization of new and more efficient organic dyes for DSSCs.