Acta Phys. -Chim. Sin. ›› 2019, Vol. 35 ›› Issue (3): 275-283.doi: 10.3866/PKU.WHXB201804231

Special Issue: Nonfullerene Organic Solar Cells

• ARTICLE • Previous Articles     Next Articles

Effects of Terminal Groups in Third Components on Performance of Organic Solar Cells

Peiyao XUE1,Junxiang ZHANG2,Jingming XIN3,Jeromy RECH4,Tengfei LI1,Kaixin MENG1,Jiayu WANG1,Wei MA3,Wei YOU4,Seth R. MARDER2,Ray P. S. HAN1,*(),Xiaowei ZHAN1,*()   

  1. 1 Department of Materials Science and Engineering, College of Engineering, Key Laboratory of Polymer Chemistry and Physics of Ministry of Education, Peking University, Beijing 100871, P. R. China
    2 Center for Organic Photonics and Electronics, School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332-0400, USA
    3 State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an 710049, P. R. China
    4 Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3290, USA
  • Received:2018-03-29 Published:2018-08-28
  • Contact: Ray P. S. HAN,Xiaowei ZHAN;
  • Supported by:
    the National Natural Science Foundation of China(21734001);the National Natural Science Foundation of China(51761165023);the National Natural Science Foundation of China(21504066);the National Natural Science Foundation of China(21534003);the Department of the Navy, U.S.(N00014-14-1-0580);the Department of the Navy, U.S.(N00014-16-1-2520);the Ministry of Science and Technology, China(2016YFA0200700);the Natural Science Foundation, U.S.(DMR-1507249);the Natural Science Foundation, U.S.(CBET-1639429)


Ternary blends have been considered as an effective approach to improve power conversion efficiency (PCE) of organic solar cells (OSCs). Among them, the fullerene-containing ternary OSCs have been studied extensively, and their PCEs are as high as over 14%. However, all non-fullerene acceptor ternary OSCs are still limited by their relatively lower PCEs. In this work, we used wide-bandgap benzodithiophene-difluorobenzotriazole copolymer FTAZ as the donor, low-bandgap fused-ring electron acceptor (FREA), fused tris(thieno- thiophene) end-capped by fluorinated 1, 1-dicyanomethylene-3-indanone (FOIC) as acceptor, and two medium-bandgap FREAs, indaceno-dithiophene end- capped by 1, 1-dicyanomethylene-3-indanone (IDT-IC) and indacenodithiophene end-capped by 1, 1-dicyanomethylene-3-benzoindanone (IDT-NC), as the third components to fabricate the ternary blends FTAZ:FOIC:IDT-IC and FTAZ:FOIC:IDT-NC, and investigated the effects of the third components on the performance of ternary OSCs. Both IDT-IC and IDT-NC are based on the same indacenodithiophene core but contain different terminal groups (phenyl and naphthyl). Relative to IDT-IC with phenyl terminal groups, IDT-NC with naphthyl terminal groups has extended π-conjugation, down-shifted lowest unoccupied molecular orbital (LUMO), red-shifted absorption and higher electron mobility. The binary devices based on the FTAZ:FOIC, FTAZ:IDT-IC and FTAZ:IDT-NC blends exhibit PCEs of 9.73%, 7.48% and 7.68%, respectively. Compared with corresponding binary devices, both ternary devices based on FTAZ:FOIC:IDT-IC and FTAZ:FOIC:IDT-NC exhibit better photovoltaic performances. When the IDT-IC weight ratio in acceptors is 50%, the FTAZ:FOIC:IDT-IC ternary devices exhibit the best PCE of 11.2%. The ternary-blend OSCs yield simultaneously improved open-circuit voltage (VOC), short-circuit current density (JSC) and fill factor (FF) compared with the binary devices based on FTAZ:FOIC. The higher VOC is attributed to the higher LUMO energy level of IDT-IC compared with FOIC. The improved JSC is attributed to the complementary absorption of FOIC and IDT-IC. The introduction of IDT-IC improves blend morphology and charge transport, leading to higher FF. The FTAZ:FOIC:IDT-NC system yields a higher PCE of 10.4% relative to the binary devices based on FTAZ:FOIC as the active layer. However, the PCE of the FTAZ:FOIC:IDT-NC-based ternary devices is lower than that of the FTAZ:FOIC:IDT-IC-based ternary devices. Compared with the binary devices based on FTAZ:FOIC, in FTAZ:FOIC:IDT-NC-based ternary devices, as the ratio of the third component increases, the VOC increases due to the higher LUMO energy level of IDT-NC, the FF increases due to optimized morphology and improved charge transport, while the JSC decreases due to the overlapped absorption of FOIC and IDT-NC. The terminal groups in the third components affect the performance of the ternary OSCs. The lower LUMO. energy level of IDT-NC is responsible for the lower VOC of the FTAZ:FOIC:IDT-NC devices. The red-shifted absorption of IDT-NC leads to the overlapping of the absorption spectra of IDT-NC and FOIC and lower JSC. On the other hand, replacing the phenyl terminal groups by the naphthyl terminal groups influences the π-π packing and charge transport. The FTAZ:FOIC:IDT-NC blend exhibits higher electron mobility and more balanced charge transport than FTAZ:FOIC:IDT-IC, leading to a higher FF.

Key words: Fused-ring electron acceptor, Non-fullerene acceptor, Organic solar cell, Terminal-group effect, Ternary blend