Molecular Modeling of Pentacyclic Aromatic Bislactam-Based Small Donor Molecules by Altering Auxiliary End-Capped Acceptors to Elevate the Photovoltaic Attributes of Organic Solar Cells

[Image: see text] Small-molecule (SM)-based organic solar cells (OSCs) have dominated the photovoltaic industry on account of their efficient optical and electronic properties. This quantum mechanical study addresses a DFT study of pentacyclic aromatic bislactam (PCL)-based small molecules for extremely proficient OSCs. Five novel small molecules (PCLM1–PCLM5) retaining the A−π–A−π–D−π–A−π–A arrangement were fabricated from the reference PCLR. At the MPW1PW91/6-31G** level of theory, detailed profiling of these novel molecules was performed by accurately following DFT, along with the time-dependent density functional theory (TD-DFT) hypothetical simulations to analyze the UV–visible absorption (λ(max)), light-harvesting efficiency (LHE), dipole moment (μ), fill factor (FF), open-circuit voltage (V(OC)), power conversion efficiency (PCE), frontier molecular orbitals (FMOs), binding energy (E(b)), density of states (DOS), electrostatic potential (ESP), and transition density matrix (TDM) plots. Alteration of peripheral acceptors in all of the molecular structures drastically modified their charge-transfer properties, such as a strong light-harvesting capability in the range of 0.9993–0.9998, reduced exciton E(b) (from 0.34 to 0.39 eV), a reduced bandgap (E(g)) in the range of 1.66–1.99 eV, an elevated λ(max) (775–959 nm) along with a higher μ in the solvent phase (1.934–7.865 D) when studied in comparison with PCLR, possessing an LHE of 0.9986, an E(b) of 0.40, an E(g) 2.27 eV, λ(max) at 662 nm, and a μ of 0.628 D. The FMO analysis revealed the uniform dispersal of charge density entirely along the highest occupied (HOMO) and lowest unoccupied (LUMO) molecular orbitals in newly constructed moieties. Electron as well as hole mobility rates, V(OC), FF, and PCE of all novel molecules (PCLM1–PCLM5) were higher as compared with those of PCLR, ultimately making them exceptional candidates for solar devices. Focusing on the outcomes, terminal acceptor modification was found to be a suitable method for the development of highly tuned OSCs in the future.