Solar energy is safe, green, and clean. Solar cell which converts sunlight to electricity through photovoltaic effect is an ideal technology to use solar energy. Compared with traditional silicon-based solar cells, organic solar cells (OSCs) possess some merits, such as low cost, light weight, portability, flexibility and semi-transparency. The active layer in OSCs consists of electron donor and electron acceptor. During last 2 decades, fullerene derivatives have been prevailing electron acceptor materials in OSCs. Nevertheless, fullerene acceptors suffer from some drawbacks, such as weak absorption in the visible region, limited tunability of energy levels, thermal instability, and photochemical instability. Therefore, it is a challenge to develop high-performance acceptor materials for OSCs.
Since 2006, Xiaowei Zhan group, in the Department of Materials Science and Engineering, College of Engineering, Peking University, have been working on high-performance nonfullerene acceptor materials. In 2007, they reported the first rylene diimide polymer acceptor (J. Am. Chem. Soc., 2007, 129, 7246-7247, cited 830 times). In 2015, Xiaowei Zhan group proposed the new concept of “fused-ring electron acceptors (FREAs)”, and invented novel FREAs, such as ITIC, a star molecule (Adv. Mater., 2015, 27, 1170–1174, cited 580 times). Their original work has attracted extensive attention, and dozens of well-known research groups across the world have used these FREAs like ITIC. In the past three years, thanks to the emergence of ITIC-like FREAs, the efficiency of nonfullerene OSCs rapidly increased from <7% to nearly 15%, outperforming their fullerene counterparts. Now, the field of OSCs is inaugurating the nonfullerene era. To date, Zhan group has published over 90 high-quality papers (including 17 ESI hot papers, 30 ESI highly cited papers) in the field of nonfullerene OSCs, which were cited over 10,000 times. Both their publication number and citations rank No. 1 in the field of nonfullerene OSCs.
Most recently, Xiaowei Zhan and collaborators published an invited review entitled “Nonfullerene acceptors for organic solar cells” in Nature Reviews Materials (2018, 3, 18003). This review systematically summarized the research progress in the two most representative classes of nonfullerene acceptors: rylene diimides and FREAs, discussed the structure-property relationship of nonfullerene acceptors, and addressed the remaining challenges and the key research directions in the near future.
This work was supported by National Nature Science Foundation of China.
The structure of a bulk-heterojunction OSC and chemical structure of star molecule ITIC