Recent progress in non-fused ring electron acceptors for high performance organic solar cells

In recent years, significant progress has been witnessed in organic solar cells (OSCs), which is mainly attributed to the new active layer materials design, especially fused ring acceptors. However, the majority of fused-ring acceptors suffer from complicated synthetic procedures and unsatisfactory reaction yields and thus high preparation cost. It is difficult to reconcile with the necessity for OPVs to demonstrate the low cost advantage compared with other photovoltaic technologies such as silicon or perovskite solar cells, thus significantly limiting the future application of OSCs. Therefore, it is necessary to develop high efficiency but low cost acceptor materials, i.e. non-fused ring electron acceptors (NFREAs). In this review, the recent development of NFREAs from the viewpoint of materials design is discussed. In the first and second sections, NFREAs with different central cores are reviewed. Then, the progress of fully non-fused NFREAs is summarized. Finally, an outlook on the remaining challenges to the field is provided.