Spectroscopic investigations of copolymers incorporating various thiophene and phenylene monomers

International audienceExperimental and theoretical studies are combined in order to describe copolymers involving various thiophene and phenylene monomers (TBT). The copolymers structures are confirmed and their optical properties are examined. The incorporation of a block unit, such as biphenylene, bipyridine or anthracene into the full conjugated backbone has a significant effect not only on the structural and vibrational properties of the compound but also on its optical behavior, resulting in different electronic transitions and emission colors from blue to blue-greenish and green. Therefore, a better correlation between photoluminescence and Raman vibrational modes assigned to the phonon emission is established. Theoretical studies, based mainly on density functional theory (DFT) calculations, are performed to explain the effect of the block unit incorporation in the optical property modifications. As a result, the blue shift is related to a less planar structure of the copolymer

Theoretical study of new donor-π-Acceptor compounds based on Carbazole, Thiophene and Benzothiadiazole for photovoltaic application as dye-sensitized solar cells

International audienceIn 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

The computational study of the electronic and optoelectronics properties of new materials based on thienopyrazine for application in dye solar cells

International audienceTo understand the importance of the organic material of type donor-π-acceptor dyes (D-π-A), used for dye-sensitized solar cells (DSSCs), we present in this paper the result of six compounds based on thienopyrazine (D1-D6) studied by density functional theory (DFT) and time dependent DFT (TD-DFT) approaches to shed light on how the π-conjugation order influence the performance of the dyes. The electron acceptor (anchoring) group was 2-cyanoacrylic acid for all dyes whereas the electron-donor unit varied and the influence was investigated. The theoretical results have shown that TD-DFT calculations using the Coulomb attenuating method CAM-B3LYP with the polarized split-valence 6-31G (d, p) basis sets and the polarizable continuum model (PCM) were reasonably capable of predicting the excitation energies, the absorption and the emission spectra of the dyes. The study of structural, electronic and optical properties for these dyes could help to design more efficient functional photovoltaic organic materials. Key parameters in close connection with the short-circuit current density (Jsc), including light harvesting efficiency (LHE), injection driving force (ΔGinject) and total reorganization energy (ltotal), were discussed

Theoretical Studies by Using the DFT and TD-DFT of the effect of the bridge formed of thienopyrazine in solar cells

International audienceTo understand the effect of the bridge part in organic solar cells, in the first we have done the synthesis of two compounds for objective to predict experimentally theirs properties optoelectronics and to comparing theses properties with those obtained by different functional ( B3LYP, CAMB3LYP, PBEPBE, B3PW91) therefore to find the appropriate quantum method for reproducing the optoelectronics properties, in the second part we have made theoretical studies of six compounds of thienopyrazine derivatives, by using DFT/B3LYP/6-31 G(d, p) level for optimize the geometry structures and predict the electronics properties. The time-dependent DFT (TD-DFT/CAM-B3LYP /6-31G(d,p)) level has been used for predict the excitations properties. This study includes the predicting of the energy of HOMO and LUMO level, the gap energy, the Voc (open circuit voltage) and λmax of absorption and other quantum parameters. The result shows that the performance of solar cells favors better with increasing the π conjugated of the bridge