Reactivity-based descriptors for donor-acceptor efficiency in organic solar cells

Non-fullerene acceptors have significantly improved the efficiency of organic solar cells (OSC), with Y6-based materials demonstrating superior performance. However, the molecular-level mechanisms of charge transfer (CT) and donor-acceptor interactions remain unclear. This study employs density functional theory and local reactivity descriptors to investigate charge transport pathways in donor-acceptor systems. By exploring charge transport sites, we highlight electronic features that drive CT efficiency and donor:acceptor performance. Results reveal balanced electron and hole site accessibility of Y6, contributing to its high efficiency by diminishing trapping effects in the active layer. Donors such as D18 and PM6 show strong donation tendencies, while the lower performance of HFQx-T:BZIC is linked to unfavorable electrostatic interactions and inefficient charge transport pathways. The donor-acceptor maps highlight that efficient pairs display well-separated CT indices, whereas low-performance systems exhibit overlapping characteristics. These findings highlight how low-cost molecular descriptors can effectively predict CT sites and guide material selection for OSC.