Ternary Organic Solar Cells with Efficiency >16.5% Based on Two Compatible Nonfullerene Acceptors

A ternary structure has been demonstrated as being an effective strategy to realize high power conversion efficiency (PCE) in organic solar cells (OSCs); however, general materials selection rules still remain incompletely understood. In this work, two nonfullerene small-molecule acceptors 3TP3T-4F and 3TP3T-IC are synthesized and incorporated as a third component in PM6:Y6 binary blends. The photovoltaic behaviors in the resultant ternary OSCs differ significantly, despite the comparable energy levels. It is found that incorporation of 15% 3TP3T-4F into the PM6:Y6 blend results in facilitating exciton dissociation, increasing charge transport, and reducing trap-assisted recombination. All these features are responsible for the enlarged PCE of 16.7% (certified as 16.2%) in the PM6:Y6:3TP3T-4F ternary OSCs, higher than that (15.6%) in the 3TP3T-IC containing ternary devices. The performance differences are mainly ascribed to the compatibility between the third component and the host materials. The 3TP3T-4F guest acceptor exhibits an excellent compatibility with Y6, tending to form well-mixed phases in the ternary blend without disrupting the favored bicontinuous transport networks, whereas 3TP3T-IC displays a morphological incompatibility with Y6. This work highlights the importance of considering the compatibility for materials selection toward high-efficiency ternary organic OSCs.