Dual-functional ambipolar non-fused ring electron acceptor as third component and designing similar molecular structure between two acceptors for high-performance ternary organic solar cells

Non-fused ring electron acceptors (NFREAs) are attractive for organic solar cells (OSCs) due to their lower cost and easier synthesis step compared with fused ring type counterparts. Herein, we demonstrate ternary OSCs with two tailor-made NFREAs to improve the efficiency of NFREA-based OSCs. An ambipolar NFREA with dual functions of both electron accepting and donating is employed as third component in ternary blend to provide smooth multiple charge transfer routes without accumulation, and to generate additional photoexcited carriers at the two NFREAs interface. Time-resolved photoluminescence and transient absorption spectroscopy tests confirm the charge transfer between two NFREAs besides between donor and NFREAs. Both space-charge-limited-current mobility and field-effect mobility reveal the ambipolar transport in the third component. In addition, two NFREAs are designed with similar molecular structure to improve the miscibility, in turn, to form homogenously mixed phase with enhanced molecular packing. As a result, the ternary OSC with two NFREAs yields an impressive power conversion efficiency of 15.01%, which is significantly higher than that of binary devices. This work provides an effective strategy to improve the efficiency of NFREA-based OSCs by employing dual-functional ambipolar NFREA and designing similar molecular structure between two NFREAs.