Engineering of A-π-D-π-A system based non-fullerene acceptors to enhance the photovoltaic properties of organic solar cells; A DFT approach

Abstract

In photovoltaic mechanization, central core alteration is an efficient tool to regulate photo-electronic features of the organic photovoltaic cells. Four fullerene free π-conjugated acceptor moieties (D1-D4) in the acceptor–donor-acceptor (A-D-A) geometries were constructed, by using quantum mechanical reproduction, from the reported acceptor molecule R with 10.27% and 13.97% solar efficiency for single and tandem organic photovoltaic cells. For the exhaustive investigation of reference molecule R and all other modified compounds through time dependent self-consistent field (TD-SCF) and density functional theory (DFT) method, MPW1PW91 functional with 6-31G (d,p) basis set was elected. Fundamental details about charge delocalization between the reference and constructed structures were obtained. Amongst all, D4 molecule elucidates the most shrunk band-gap of 2.24 eV, maximum absorption at 697 nm in chlorobenzene solvent, and a smaller binding energy of 0.47 eV that helps to effectively transmit the electron densities from bonding orbitals/HOMO to anti-bonding orbitals/LUMO. Electron and hole mobilities revealed by all constructed molecules were found to be lower when contrasted to the reference molecule R. Upon testing all modified molecules with polymer donor PTB7-Th, D3 moiety gave a higher open-circuit photo-voltage (Voc) value (1.23 eV) as compared to all other molecules, which shows that it has higher electronic charge transfer than other molecules. This current work indicates that by replacing the central part of R with some prominent donor cores, we can efficiently tune the binding energy, open-circuit photo-voltage, frontier molecular orbitals, absorption spectra, band-gap, and reorganization energy in the thus constructed structures. Thus in the future, tailored compounds ought to be suggested for the manufacture of OSCs with high solar efficiency.