Dithienosilole-benzothiadiazole-based ternary copolymers with a D sub(1)-A-D sub(2) -A structure for polymer solar cells

• Published in: Polymer chemistry 2015-05, Vol.6 (22), p.4154-4161
• Main Authors: Huang, Xuelong, Zhang, Guichuan, Zhou, Cheng, Liu, Liqian, Jin, Yaocheng, Liu, Shengjian, Ying, Lei, Huang, Fei, Cao, Yong
• Format: Article
• Language: English
• Subjects: Copolymerization; Copolymers; Energy conversion efficiency; Optical properties; Optimization; Photovoltaic cells; Solar cells; Strategy
• ISSN: 1759-9954; 1759-9962
• DOI: 10.1039/c5py00201j

A series of narrow band gap conjugated copolymers comprising two electron-rich (donor, D) and one electron-deficient (acceptor, A) moieties regularly alternating along the polymer backbone were designed and synthesized. The ternary copolymers with the repeating unit in a D sub(1)-A-D sub(2) -A manner were constructed by copolymerizing a bisstannyled-D sub(1) (D sub(1) = cyclopentadithiophene or benzodithiophene-derivatives) and a dibromo-monomer (Br-A-D sub(2)-A-Br, D sub(2) = dithienosilole, A = benzothiadiazole) through a palladium-catalyzed Stille polymerization. It was recognized that the optical properties, frontier molecular orbital energy levels and the photovoltaic performance of the resulting copolymers can be influenced by modifying the copolymerized D sub(1) moiety. By carefully optimizing the electron-donating behaviours and substitutions of the D sub(1) unit, bulk-heterojunction solar cells with a power conversion efficiency of 4.11% were achieved based on an inverted device configuration of ITO/PFN-OX/PBDT-O-ADA:PC sub(71)BM/MoO sub(3 )/Al. These results demonstrated that the construction of regularly alternating narrow band gap conjugated ternary copolymers can be an effective strategy for the development of electron-donating materials for polymer solar cells.