Unveiling the influence of end-capped acceptors modification on photovoltaic properties of non-fullerene fused ring compounds: a DFT/TD-DFT study

Abstract

Herein, unique A–D–A configuration-based molecules (NBD1–NBD7) were designed from the reference compound (NBR) by utilizing the end-capped acceptor modification approach. Various electron-withdrawing units –F, –Cl, –CN, –NO₂, –CF₃, –HSO₃, and –COOCH₃, were incorporated into terminals of reference compound to designed NBD1–NBD7, respectively. A theoretical investigation employing the density functional theory (DFT) and time-dependent DFT (TD-DFT) was performed at B3LYP/6-311G(d,p) level. To reveal diverse opto-electronic and photovoltaic properties, the frontier molecular orbitals (FMOs), absorption maxima (λ_max), density of states (DOS), exciton binding energy (E_b), open-circuit voltage (V_oc) and transition density matrix (TDM) analyses were executed at the same functional. Moreover, the global reactivity parameters (GRPs) were calculated using the HOMO–LUMO energy gaps from the FMOs. Significant results were obtained for the designed molecules (NBD1–NBD7) as compared to NBR. They showed lesser energy band gaps (2.024–2.157 eV) as compared to the NBR reference (2.147 eV). The tailored molecules also demonstrated bathochromic shifts in the chloroform (671.087–717.164 nm) and gas phases (623.251–653.404 nm) as compared to NBR compound (674.189 and 626.178 nm, respectively). From the photovoltaic perspectives, they showed promising results (2.024–2.157 V). Furthermore, the existence of intramolecular charge transfer (ICT) in the designed compounds was depicted via their DOS and TDM graphical plots. Among all the investigated molecules, NBD4 was disclosed as the excellent candidate for solar cell applications owing to its favorable properties such as the least band gap (2.024 eV), red-shifted λ_max in the chloroform (717.164 nm) and gas (653.404 nm) phases as well as the minimal E_b (0.126 eV). This is due to the presence of highly electronegative –NO₂ unit at the terminal of electron withdrawing acceptor moiety, which leads to increased conjugation and enhanced the intramolecular charge transfer (ICT) rate. The obtained insights suggested that the designed molecules could be considered as promising materials for potential applications in the realm of OSCs.