Strategies toward the end-group modifications of indacenodithiophene based non-fullerene small molecule acceptor to improve the efficiency of organic solar cells; a DFT study

Abstract

In this study, five indacenodithiophene (IDT) core-based small acceptor molecules (AT1-AT5) were designed by replacing the terminal acceptor groups of reference molecule (ATR) with five different electron-withdrawing groups. The density functional theory (DFT) was employed to investigate the photovoltaic properties of the newly developed molecules. The MPW1PW91/6-31G (d,p) methods have been used to investigate the effects of different terminal acceptor moieties on the FMOs, density of states (DOS), maximum absorption, the reorganization energies, transition density matrix, dipole moment,and open-circuit voltage (VOC) and then all these properties of modified molecules are compared with reference molecule. The VOC of all studied molecules is computed with respect to donor PTB7-Th. Many of these properties have been improved considerably in modified molecules. Amongst, all the developed chromophores, the AT4 molecule revealed the highest λmax (802 nm), a reduced bang-gap of 2.01 eV, and smaller electron and hole reorganization energies (0.0056611 eV and 0.0063966 eV, respectively), lowest first excitation energy (1.54 eV), and greatest electron affinity (3.44 eV). While AT3 has the least exciton binding energy (0.46 eV) and significant dipole moment (0.69 D) than all other tailored structures. Thus, these results demonstrate that the novel molecules are convincing factors in constructing the extremely effective NFAs photovoltaic cells.