Theoretical enhancement of the electronic and optical properties of a new D-π-A-π-D synthesized donor molecule for a new generation of fullerene-based bulk heterojunction (BHJ) for new organic solar cells devices.

Herein, photophysical and electronic properties of a newly synthesized D-π-A-π-D benzothiadiazole derivative referred to 'R' molecule, were theoretically improved. Using Density Functional Theory (DFT), and it extended TDDFT methodologies, a news SMi (i = 1-4) benzothiadiazole derivatives are designed and studied by the modification of the acceptor (A) ring. Theoretical calculations show that going from R molecules to SMi ones, an intramolecular charge transfer is obtained. Indeed, the calculated dipole moment variation (μ) between the ground and the first excited state increases. Consequently, an enhancement of the absorption in the visible part, and a reduction of the calculated optical band gap and the energy gap HOMO-LUMO are obtained. Furthermore, the calculated power conversion efficiency (PCE) factor of the bulk-heterojunction (BHJ) based on the investigated molecules (R and SMi, i = 1-4), as donor material and the fullerene (C60) as an acceptor one, increases drastically from 8% for R molecule to 13.5% for SM3 one according to Marks diagram. Finally, reduced density gradient analysis (RDG) analysis on the SM3-C60 designed composite proves the weak Vander-Waals interactions between the donor SM3 and the chosen acceptor C60.