New organic compounds based on N-fluorene-carbazole moiety fordye-sensitized solar cells. Computational study

In this workwe areinterested tothe theoretical study ofnew organic dyescomprising N-fluorene-carbazole moiety as an electron-donating group, several unit based on thiophene(Th), dithiophene(2Th), 3.4-ethylenedioxythiophene (EDOT), dithienothiophene(DTT) or 4-dicyanomethylene-4H-cyclopenta [2.1-b; 3-4- b']-dithiophene (CDM) and4H-cyclopenta [2.1-b; 3.4-b']-4-dithiophene sulfone(CPDS) as pi-spacer and a cyanoacrylic acid as the anchoring group in the molecular framework. For identical electron donor groups, we introduced different pi-spacer to examine their effect on the structural and electronic properties Thisstudywasperformedby the density functional theory (DFT) method at B3LYP level the 6-31G( d,p). The HOMO, LUMO, band gap energy, ionization potentials (IPs), electron affinities (EAs) of these dyeshas been calculated and reported in this paper. The electronic absorption and emission spectra of these dyes are studied by Time-Dependent Density Functional Theory (TD-DFT) calculations. Our aim is first to confirm and improve properties of these studied dyes. Second, to explore their electronicand spectroscopic properties on the basis of the DFT quantum chemical calculations. Third, to elucidate the parameters that influence the photovoltaic efficiency toward better understanding of the structure-property relationships. We think that the presented study of structural, electronic and optical properties for these dyes could help to design more efficient functional photovoltaic organic materials.