A Quinoxaline‐Based D–A Copolymer Donor Achieving 17.62% Efficiency of Organic Solar Cells

• Published in: Advanced materials (Weinheim) 2021-06, Vol.33 (23), p.e2100474-n/a
• Main Authors: Zhu, Can, Meng, Lei, Zhang, Jinyuan, Qin, Shucheng, Lai, Wenbin, Qiu, Beibei, Yuan, Jun, Wan, Yan, Huang, Wenchao, Li, Yongfang
• Format: Article
• Language: English
• Subjects: Agglomeration; alkyl‐substituted fluorothiophene side chains; Carrier recombination; conjugated D–A copolymer donors; Copolymers; Current carriers; difluoroquinoxaline A‐unit; Energy conversion efficiency; Energy levels; Hole mobility; Materials science; Morphology; Photovoltaic cells; Quinoxalines; side‐chain engineering; Solar cells
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.202100474

Side‐chain engineering has been an effective strategy in tuning electronic energy levels, intermolecular interaction, and aggregation morphology of organic photovoltaic materials, which is very important for improving the power conversion efficiency (PCE) of organic solar cells (OSCs). In this work, two D–A copolymers, PBQ5 and PBQ6, are designed and synthesized based on bithienyl‐benzodithiophene (BDTT) as the donor (D) unit, difluoroquinoxaline (DFQ) with different side chains as the acceptor (A) unit, and thiophene as the π‐bridges. PBQ6 with two alkyl‐substituted fluorothiophene side chains on the DFQ units possesses redshifted absorption, stronger intermolecular interaction, and higher hole mobility than PBQ5 with two alkyl side chains on the DFQ units. The blend film of the PBQ6 donor with the Y6 acceptor shows higher and balanced hole/electron mobilities, less charge carrier recombination, and more favorable aggregation morphology. Therefore, the OSC based on PBQ6:Y6 achieves a PCE as high as 17.62% with a high fill factor of 77.91%, which is significantly higher than the PCE (15.55%) of the PBQ5:Y6‐based OSC. The PCE of 17.62% is by far one of the highest efficiencies for the binary OSCs with polymer donor and Y6 acceptor. Two D–A copolymers, PBQ5 and PBQ6, are designed and synthesized based on difluoroquinoxaline (DFQ) units with different side chains. The organic solar cell (OSC) based on PBQ6 as donor and Y6 as acceptor achieves a high power conversion efficiency of 17.62%, which is one of the highest efficiencies for binary OSCs with a polymer donor and Y6 acceptor.