High carrier mobility is beneficial to increase the active-layer thickness while maintaining a high fill factor, which is crucial to further improve the light harvesting and organic photovoltaic efficiency. The aim of this Perspective is to elucidate the electron transport mechanisms in prototypical non-fullerene (NF) acceptors through our recent theoretical studies. The electron transport in A-D-A small-molecule acceptors (SMAs), e.g., ITIC and Y6, is mainly determined by end-group π-π stacking. Relative to ITIC, the angular backbone along with more flexible side chains leads to Y6 having a closer stacking and enhanced intermolecular electronic connectivity. For polymerized rylene diimide acceptors, to achieve high electron mobilities, they need to simultaneously increase intramolecular and intermolecular connectivity. Finally, finely tuning the π-bridge modes to enhance intramolecular superexchange coupling is essential to develop novel polymerized A-D-A SMAs.