Tuning of diphenylamine subphthalocyanine based small molecules with efficient photovoltaic parameters for organic solar cells

In this theoretical research, four donor molecules with diphenylamine subphthalocyanine (SubPc) as a common core, flanked with various electron-withdrawing groups at the central position containing Methyl-2-cyanoacrylate in C1, 3-methyl-5-methylene-2-thioxothiazolidin-4-one in C2, 2-(2-methylene-1-oxo-1H-inden-3 (2H)-ylidene) malononitrile in C3, and Methyl-2-(5-methylene-4-oxo-2-thioxothiazoliden-3-yl) acetate in C4, have been designed. To analyze photovoltaic applications of all the studied molecules (C1-C4), quantum chemical simulations i.e., absorption profiles, frontier molecular orbitals (FMOs), the density of states (DOS), transition density matrix, and open-circuit voltage, have been performed availing DFT and TD-DFT approach with selected B3LYP functional /6-31G (d,p) level of theory. Among all the substituted molecules, C3 revealed highest molar absorption coefficient (601 nm), efficient electron density transfer in FMOs, and lowest energy band gap (1.70 eV) owing to the elongated conjugation along with the compelling electron-withdrawing nature of its axial acceptor moiety. All investigated molecules showed profound peaks in the visible region of the absorption spectrum as well as had low electron and hole mobilities in contrast to that of the reference (R) molecule. The observed binding energies (in electron-volt) of C2 (0.67), C3 (0.10), and C4 (0.47) molecules are found to be lower than R. Hence, these findings reveal that all designed candidates (C1-C4) could be effective and favorable applicants to enhance the energy efficiency of small molecule (SM) based organic solar cells (OSCs).