Abstract
In this study, we have designed a series of novel double organic D-π-A (electron donor-π-conjugated-acceptor) based on Carbazole, Thiophene and Benzothiadiazole. The optimized structures and optoelectronic properties of these dyes have been investigated by using the Density Functional Theory DFT/B3LYP/6-31G (d, p) method and Time Dependant Density Functional Theory (TD/DFT) calculations. These dyes consist of electron-donor (Carbazole-3,4-Ethylenedioxythiophene) and-acceptors/anchoring (Benzothiadiazole and Cyanoacrylic), connected by the π-conjugated linker as an electron donor spacer constituted of Thiophene and Phenylene units. The calculated geometries indicate that these dyes have coplanar structures. The LUMO and HOMO energy levels of these dyes can ensure positive effect on the process of electron injection and dye regeneration. In order to predict the band gaps for guiding the synthesis of novel materials with low band gaps, we apply quantum-chemical techniques to calculate the band gaps in several oligomers. The trend of the calculated HOMO-LUMO (Egap) gaps nicely compares with the spectral optical data. A low band gap will be expected in polymers containing double donor-acceptor (D-A) repeating units. The bridging effect by C=C(CN)2 on the optoelectronic properties of the studied compounds is investigated. The calculated results of these dyes demonstrate that these compounds can be used as potential sensitizers for TiO2 nanocrystalline solar cells.