Tuning the optoelectronic properties of benzodithiophene based donor materials and their photovoltaic applications

To improve the quantum efficiency and device performance of OSCs, four new BDTS-2DPP based donor molecules were designed, flanked with variable non-fullerene end-capped acceptor units namely, 2-methylenemalanonitrile (BDTS1), methyl 2-cyanoacrylate (BDTS2), 2-(5,6-difluoro-2-methylene-3-oxo-2,3-dihydroinden-1ylidene)malononitrile (BDTS3), and 3-methyl-5-methylene-2-thioxothiazolidin-4-one (BDTS4). A detailed computational study was carried out on designed molecules using DFT and TD-DFT to examine their optoelectronic properties. Optical parameters such as maximum absorption, dipole moments, excitation energies, etc. were recorded at excited optimized states using dichloromethane solvent. Next, to analyze the charge density distribution and energy level differences, DOS and FMOs were interpreted. Reorganization energies were calculated to find out electron-hole mobilities and exciton coherence is indicated by TDM maps. The results illustrate that these molecules (BDTS1-BDTS4) excelled the reference molecule in all the computed properties. BDTS3 exhibited the highest lambda max (865 nm) and least band gap (1.80 eV) while BDTS1 endured the highest electron-hole mobilities and open-circuit voltage (1.61 eV). All the theoretically computed parameters suggest that these designed molecules could be used as proficient donor materials in OSCs.