Recent progress on all-small molecule organic solar cells using small-molecule nonfullerene acceptors

Recently, solution-processed organic solar cells combining small-molecule donor and nonfullerene acceptor have achieved breakthrough results with the certified efficiency over 15%. These impressive progresses are driven by the concerted efforts of modifying the donor and acceptor materials and optimizing the morphology. Considering the defined chemical structures and easily tuned properties of small-molecule materials, it is of great necessity and importance to pay more attentions on the topic of all-small molecule organic solar cells. Here, we summarize the recent progress of all-small molecule organic solar cells from the prospect of materials' evolutions and expect to provide some hints for its future developments. The involved small-molecule donors including oligothiophene-, benzodithiophene-, naphthodithiophene-, and porphyrin-based materials are discussed to illustrate the relationship of chemical structures, properties, and device performance. Then, the small-molecule nonfullerene acceptors in all-small molecules organic solar cells are discussed to highlight their vital role. Finally, we will present the challenges and future of this research area.