Examining the Impact of 3D Multi‐Arm Small Molecules on PM6:Y6 Blend Reveals the Key Requirements for Their Electronic Properties

While the emergence of PM6:Y6 active layer re‐energized the organic photovoltaic community, excessive aggregation of Y6 molecules induced by their strong intermolecular interactions has limited the performance of PM6:Y6‐based organic solar cells (OSCs). Adding 3D multi‐arm small‐molecule acceptors is an effective strategy to inhibit such aggregation. However, to maximize OSC efficiency, these molecules should also contribute to the electronic processes. Here, by taking a benzotriazole‐based 3D four‐arm small molecule (i.e., SF‐BTA1) as representative example, we combine molecular dynamics simulations and density functional theory calculations to examine the molecular‐scale impact of 3D multi‐arm small molecules on morphological characteristics (especially at the nanoscale) and electronic properties of PM6:Y6 blends. By considering the intermolecular packing distances, density, and patterns among PM6, Y6, and SF‐BTA1 components, exciton transfer rates from SF‐BTA1 to Y6 or PM6, charge transfer rates from Y6 or PM6 to SF‐BTA1, electron/hole transfer rates among adjacent Y6/PM6 pairs, and radiative and non‐radiative recombination processes, we draw a comprehensive picture that describes how 3D multi‐arm small molecules improve morphological and electronic properties of PM6:Y6 blends and thus the OSC efficiency. Furthermore, successful rationalization of these aspects allows us to point out key requirements regarding the electronic properties of 3D multi‐arm small molecules.