Non-fullerene organic small molecule electron-acceptors

To achieve high efficiency organic solar cells (OSCs), the development of donor and acceptor materials for the bulk-heterojunction (BHJ) blend is the most important part and has attracted great interest. So far, the study of donor materials is still dominant and devices with efficiency exceeded 8% are reported by many research groups. On the contrary, the developments of new acceptor materials are relatively limited, and most of them are focused on the derivatives of fullerene. Recently, organic small molecule acceptors (OSMAs), which are potential alternative to fullerene derivatives, have drawn significant interest. Compared to fullerene derivatives, OSMAs are much easier to be synthesized and purified, and the bandgap could be finely adjusted by proper molecule design. Recent reports on OSMAs show great improvement and the efficiency has reached 4%. In this review, several kinds of OSMAs, covering new molecule design and application in device fabrication are comprehensively introduced. Finally, critical challenges that determine photovoltaic performance and prospects for future directions are discussed.