Recent progress in small‐molecule donors for non‐fullerene all‐small‐molecule organic solar cells

Abstract All‐small‐molecule organic solar cells (all‐SM OSCs), with p ‐type small molecule ( p ‐SM) as donor and n ‐type small molecule ( n ‐SM) as acceptor, have drawn intensive research interests in recent years. All‐SM OSCs show advantages to their polymer counterparts, including well‐defined chemical structure, easy purification, and better repeatability in devices. The highest power conversion efficiency (PCE) of all‐SM OSCs has increased quickly to over 15% nowadays. In this review, we just summarize the progress of non‐fullerene all‐SM OSCs (NF all‐SM OSCs) in recent five years, by dividing small‐molecule donors into four categories based on the molecular segments of oligothiophene, benzo[1,2‐ b :4,5‐ b ’]dithiophene (BDT) trimer, typical BDT‐central unit connected with π‐bridges of thiophene or electron deficient acceptor units. We aim to illustrate the relationship of molecular structures, properties, and device performance of small‐molecule donors with those different molecular segments. Furthermore, the tendency of molecular design for photo‐active materials are also depicted and summarized. Finally, we give our views on the future prospects of NF all‐SM OSCs to design the next‐generation OSCs.