A nanoscale view of PM6 and Y6 bulk and interfacial structures

Control of device performance within organic photovoltaics requires a nano to molecular scale description of the device morphology. Here we describe the bulk and interface morphology of PM6:Y6 systems, enabled through virtual site coarse grained molecular dynamics. In neat film simulations, PM6 remained amorphous, while Y6 assembled into highly ordered structures. In intimately mixed blends, Y6 and PM6 cluster into segregated domains. When blend simulations started from a completely segregated state, concentration profiles show Y6 first penetrated the PM6 domain, followed by PM6 chain swelling, resulting in a mixed phase interface a few nanometers wide. After several microseconds of simulation the two blend configurations were similar in their structure. Our coarse-grained method still preserves molecular details, and we capture these details by calculating the fraction of pi-stacked conjugated rings between PM6-PM6, Y6-PM6 and Y6-Y6. Our morphology description provides details on the molecular conformations integral to understanding exciton and polaron transport and exciton separation at the interface.