<p>Molecular engineering is crucial in the design and synthesis of electron donor and acceptor materials in organic solar cells (OSCs). In particular, OSCs based on halogenated non-fullerene acceptors (NFAs) showed high power conversion efficiencies (PCEs). The PCE of iodinated NFA OSC reached 18.9%. Herein, in order to understand the impact of NFA end-group iodination on photovoltaic performance, we selected PBDB-TF as the electron donor, BO-4F and BO-4I as the NFAs. Quantum chemistry computations were employed to study the geometric configurations, electronic structures, excited-state properties and electrostatic potentials of PBDB-TF, BO-4F and BO-4I molecules, as well as their complexes PBDB-TF:NFAs constructed as interface models. Moreover, the rate constants of charge transfer (CT), exciton dissociation (ED) and charge recombination (CR) processes were analyzed. The calculation results indicate that the end-group iodination causes a slight increase in the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels, leading to slight increase in HOMO–LUMO gap. Meanwhile, iodination decreases the average electrostatic potential, enhances light absorption, causes the redshift of absorption spectrum, reduces exciton binding energy and increases the dielectric constant and CT energy. Furthermore, the end-group iodination of NFA enhances the hybridization of CT and local excitation for the lowest excited states, but also induces quasi-degenerate of low-lying excited states. Additionally, the end-group iodination increased ED, CT and CR rates. The results of this work help to understand the relationship between molecular structure, properties and photovoltaic performance, but also provide theoretical basis for the design NFAs to improve PCE of OSCs.</p>