Nonfullerene acceptors with carbon-oxygen-bridged fused nonacyclic donor units enable efficient organic solar cells

The power conversion efficiency (PCE) of an organic solar cell (OSC) mainly depends on the chemical structures and intrinsic properties of its active layer materials. The development of new nonfullerene acceptors (NFAs) has significantly boosted the PCEs of OSCs over the last decade. Herein, two carbon-oxygen-bridged fused nonacyclic donor units were developed to synthesize two NFAs, namely TTPIC-Ar and iTTPIC-Ar, respectively. The PM6:iTTPIC-Ar blend film displays clearer phase separation with subtler and narrower nanofiber structure, which shortens the exciton diffusion distance to donor/acceptor interfaces, reduces trap density and improves charge carrier mobilities in its devices, compared with the PM6:TTPIC-Ar counterpart. These features help to achieve a higher exciton dissociation probability and to inhibit charge carrier recombination, leading higher short-circuit current density and fill factor values for its OSCs. As a result, the PM6:iTTPIC-Ar-based OSC shows a higher PCE, of 12.80%, than PM6:TTPIC-Ar-based one. Our work demonstrates that designing fused ring donor units is an efficient strategy for developing high-performance NFAs and thus further improving the PCEs of OSCs.