Organic photovoltaic materials consist of electron donors and electron acceptors. In the past years, fullerenes and their derivatives have been the dominant electron acceptor materials in organic solar cells (OSCs). As fullerene acceptors have some drawbacks, such as weak absorption in the visible spectral region and limited energy level variability, development of high-performance nonfullerene acceptors is urgent and challenging in this field.
Zhan group firstly proposed the concept of “fused-ring electron acceptor (FREA)”, and designed and synthesized a series of FREAs. These FREAs present some advantages over their fullerene counterparts. In 2015 and 2016, Zhan group reported some novel FREAs based on extended fused-ring cores, such as indacenodithiophene and indacenodithieno [3,2-b] thiophene. The FREA-based OSCs exhibited power conversion efficiencies of 6-10%. See: Adv. Mater., 2015, 27, 1170-1174 (cited 240 times, ESI Hot Paper, ESI Highly Cited Paper); Energy Environ. Sci., 2015, 8, 610-616 (cited 140 times, ESI Hot Paper, ESI Highly Cited Paper); J. Am. Chem Soc., 2016, 138, 2973-2976 (cited 100 times, ESI Hot Paper, ESI Highly Cited Paper); J. Am. Chem Soc., 2016, 138, 4955-4961 (cited 120 times, ESI Hot Paper, ESI Highly Cited Paper).
In 2017, this group firstly proposed the concept “energy driver” and employed it in polymer/FREAs active layer. After the addition of tiny amount “energy driver”, the driving force for charge transfer between donor and acceptor was enhanced and the efficiency of OSCs was enhanced from 8% to 10% (Adv. Mater., 2017, 29, 1605126). They proposed the polymer donor/nonfullerene acceptor matching principle, and then used this principle to select suitable donor materials and achieved high efficiency of 11% (Adv. Mater., 2017, 29, 1604155). They designed and synthesized fused nonacyclic electron acceptors for the first time, based on which the OSCs achieved efficiency of up to 11.5% (J. Am. Chem. Soc. 2017?139 , 1336–1343). In addition, they designed and synthesized fluorinated 1,1-dicyanomethylene-3-indanone and used in synthesis of FREAs. The single-junction binary-blend OSCs based on fluorinated FREA exhibited efficiency of 12.1%, which is the highest for this type device (Adv. Mater. 2017, 29, 1700144).
Now FREAs designed by Zhan group are commercial available. Many well-known research groups across the world have already utilized these FREAs to fabricate high-efficiency OSCs, which rival the high-performance single junction OSCs based on fullerene acceptors.
This research work was supported by the National Nature Science Foundation of China and the Ministry of Science and Technology of China.
Cover paper and hot paper published by undergraduate student Boyu Jia