DFT study of opto-electronic properties of benzothiazole derivatives for use in solar cells

A variety of organic donor-acceptor-donor materials based on thienylbenzothiadiazole (BTDii=1-5) combined with different -conjugated systems are studied by density functional theory (DFT) and time-dependent DFT (TD-DFT) for the ground- and excited-state properties, respectively, using B3LYP and the 6-31G(d, p) basis set. The effect of different electron-donor groups on the structural, electronic and optoelectronic properties is studied. To provide for the bandgap and to guide the synthesis of novel low bandgap materials, we applied quantum chemistry techniques to calculate the difference in the highest occupied molecular orbital (HOMO) and lowest occupied molecular orbital LUMO energies. However, we have studied the effect of the reduction and oxidation properties on the electronic excitation transitions for all compounds. The emission energies have been obtained from TD-DFT calculations performed on the excited-state optimized S₁ geometries. The theoretical results suggest that both the introduction of electron-donor groups and the doping process contribute significantly to the electronic and optoelectronic properties of the alternating donor-acceptor-donor conjugated systems studied.