Highly crystalline two-dimensional copolymer with dominant face-on orientation for high performance polymer solar cells. (5th July 2020)

• Record Type: Journal Article
• Authors: Wang, Shih-Hao; Raja, Rathinam; Yu, Shih-Wei; Jeng, Ru-Jong; Chen, Jyh-Chien; Rwei, Syang-Peng; Wang, Leeyih
• Is Part Of: European polymer journal. Volume 134(2020)
• Publication Date: 2020-07-05
• Subjects: Two-dimensional copolymer -- Benzothiadiazole -- Polymer solar cell; Polymers -- Periodicals; Polymerization -- Periodicals; Polymères -- Périodiques; Polymérisation -- Périodiques; Polymerization; Polymers; Periodicals; Electronic journals; 547.705
• DOI: 10.1016/j.eurpolymj.2020.109799
• Languages: English
• ISSNs: 0014-3057

Abstract

Graphical abstract: Highlights: Highly crystalline two-dimensional copolymer with vinyl-terthiophene side chain was synthesized for PSCs. The substitution of fluorine atoms down shifted the HOMO/LUMO energy level. Introduction of thiophene π-spacer between 2TF and BT promoted dominant face-on orientation and high hole mobility. Abstract: We designed and synthesized a novel series of two-dimensional (2D) conjugated polymers (P1-2T, P2-2T2F and P3-4T2F) containing 2, 2′-bithiophene (2T) and 3, 3′-difluoro-2, 2′-bithiophene (2T2F) as donor units, and 4, 7-benzo[c][1, 2, 5]thiadiazole (BT) and 4, 7-di(thiophen-2-yl)benzo[c][1, 2, 5]thiadiazole (DTBT) as acceptor units appended with conjugated vinyl-terthiophene (VTT) side chain. We comprehensively investigated the effect of fluorination and thiophene (T) π-spacer on the optoelectronic properties and photovoltaic performance of the resulting copolymers. In comparison with non-fluorinated polymer P1-2T, the fluorinated polymer P2-2T2F and P3-4T2F had down shifted highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels with an enhanced absorption band. Moreover, 2D grazing incidence wide-angle X-ray scattering and space charge limited current measurement showed that the presence of thiophene π-spacer in P3-4T2F promoted dominant face-on orientation, high crystallinity and enhanced hole mobility, compared with P2-2T2F. As a result, the inverted polymer solar cell based on the P3-4T2F:PC61 BM blend exhibited a high power conversion efficiency (PCE) of 6.66% with a Jsc of 12.99 ± 0.30 mA/cm −2 . In contrast, the P1-2T:PC61 BM and P2-2T2F:PC61 BM devices without π-spacer showed a PCE of 2.22% and 0.95%, respectively. The PCE of the P3-4T2F:PC61 BM device was further improved to 6.89% by using a polyethylenimine ethoxylated (PEIE) interlayer between ITO and ZnO. This study reinvigorates the key modulation of a 2D conjugated polymer with improved photovoltaic performance.