Low Band Gap of Novel Compounds Having Triphenylamine and Oligothiophenes Based Donor-acceptor Organic Dyes for Photovoltaic Applications: A DFT-B3LYP Calculation

Abstract

Novel donor-π-acceptor (D-π-A) dyes composed of Triphenylamine having (3,4-etylenedioxythiophene) (EDOT), Oligothiophene and Benzothiadiazole were designed and studied. The optimized structures and optoelectronic properties of these dyes were 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 (Triphenylamine-3,4-Ethylenedioxythiophene-Oligothiophene) and acceptors/anchoring (Benzothiadiazole and Cyanoacrylic) : PTEBT3A, PTEBT2A, PTEBTA, PTET3A, PTET2A, PTETA, PEBTA and PBTA. The calculated geometries indicate that these dyes have coplanar structures. The LUMO and HOMO energy levels of these dyes can ensure a 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 introduction of EDOT and Benzothiadiazole units in the copolymers and the elongation of π-conjugation length of oligothiophenes led to a red-shift of absorption bands of the D-π-A dyes. The calculated HOMO-LUMO (E gap ) gaps and the wavelength of absorption spectrum (λ max ) were compared with the experimental data. It was found that a D-π-A dyes having EDOT-containing the Thiophene repeating units exhibited the low band gap and the excellent light-harvesting ability up to 795 nm. Furthermore, several quantum chemical properties, such as ionization potential (IP), electronaffinity (EA), electrophilicity index (ω), hardness (η) and chemical potential (μ) were also calculated and thoroughly discussed in the paper. The calculated results of these dyes demonstrate that these compounds can be used as potential sensitizers for TiO 2 nanocrystalline solar cells.