First principles calculations of optical and electronical properties for 2,7-carbazole derivatives as solar cells materials

A quantum chemical investigation has been performed to explore the optical and electronical properties of a series of different cores (BT, PT, and BX) molecules with oligoethylene-thiophene branches, including considered symmetry and no symmetry (for branch), for solar cell materials. The frontier molecular orbital (FMO) and band gap energy calculations for all complexes were performed at the PBE0/6-31G(d) level. The values of Eg change less than 0.1 eV depending on the different cores. On the basis of the optimized geometries, the effect of the different cores on the absorption spectra was evaluated using the TD-PBE0/6-31+G(d,p) level. BT core can make the absorption spectra have a red shift in comparison with others (PT and BX). The ionization potential (IP), electron affinity (EA), and reorganization energy (λ) were also computed. As a result of these calculations, different cores play key roles in the change the IP, EA, and λ. Moreover, the molecules with BT core have lower λe, λh, and λ than those of others. Additionally, the optical and electronical properties are similar for the molecules with symmetry (for branch) or not.