14.55% efficiency PBDB-T ternary organic solar cells enabled by two alloy-forming acceptors featuring distinct structural orders

[Display omitted] •Efficient PBDB-T ternary solar cells using two alloy-forming acceptors with distinct structural orders.•Förster resonance energy transfer between two acceptors;•Optimal phase-separation and structural order achieved with less crystalline third component;•A champion PCE of 14.55% for PBDB-T single-junction solar cells. Ternary organic solar cells (OSCs) have demonstrated great potential in boosting the power conversion efficiencies (PCEs) of single-junction devices. Screening suitable third component is crucial but challenging for different host binary OSCs. We report herein an efficient ternary strategy in achieving highly efficient PBDB-T based devices by incorporating two alloy-forming fused-ring electron acceptors (FREAs) with distinct structural orders. INPIC-Si as the third component showcases a relatively narrower bandgap and higher energy levels than the host acceptor IDTO-T-4F. Featuring good compatibility and alloy-forming blends, two FREAs generate Förster resonance energy transfer from IDTO-T-4F to INPIC-Si, facilitating efficient exciton dissociation and charge carrier transport. Importantly, the low crystalline INPIC-Si decreases the strong aggregation of PBDB‐T:IDTO-T-4F blends for optimal phase-separation and structural order. Consequently, the best PBDB‐T:IDTO-T-4F:INPIC-Si ternary OSCs deliver a champion PCE of 14.55% with simultaneously improved device parameters over binary ones. To the best of our knowledge, this performance is among the highest for PBDB-T-based ternary OSCs in literature. Our work demonstrates the incorporation of a narrow bandgap FREA with low structural order into heavily aggregated binary blends can optimize the blend morphology for reduced energy loss and significantly improved photovoltaic performance in ternary OSCs.