Difluorobenzoxadiazole-based conjugated polymers for efficient non-fullerene polymer solar cells with low voltage loss

• Published in: Organic electronics Vol. 77; p. 105541
• Main Authors: Huang, Kunxiang, Li, Miaomiao, He, Mu, Liang, Ziqi, Geng, Yanhou
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.02.2020
• Subjects: Alkylthiophene side chains; Difluorobenzoxadiazole; Non-fullerene polymer solar cells; Voltage loss; Alkylthiophene side chains; Difluorobenzoxadiazole; Voltage loss; Non-fullerene polymer solar cells
• ISSN: 1566-1199; 1878-5530
• DOI: 10.1016/j.orgel.2019.105541

Two donor-acceptor (D-A) conjugated copolymers based on difluorobenzoxadiazole (ffBX) and oligothiophenes, i.e., PffBX-2T and PffBX-TT, were designed and synthesized for polymer solar cells (PSCs). Compared to the polymers based on difluorobenzothiadiazole (ffBT) units, the two ffBX-based polymers presented identical optical bandgaps (~1.62 eV), but lower highest occupied molecular orbital (HOMO) energy levels. Owing to the down-shifted HOMO levels, the PSCs based on PffBX-2T and PffBX-TT showed lower voltage loss, and the open-circuit voltage (Voc) was ~0.1 V higher than that of the devices with the ffBT-based polymer. As a result, higher photovoltaic performance was achieved for the devices based on the ffBX-based polymers. The power conversion efficiencies (PCEs) of the non-fullerene PSCs with PffBX-2T and PffBX-TT as the donor were 8.72% and 10.12%, respectively. The superior device performance of PffBX-TT resulted from the efficient exciton dissociation and charge transport as well as weak charge recombination, which could be ascribed to the favorable face-on packing of the conjugated backbones and the desired morphology in the blend film. Our study demonstrates that difluorobenzoxadiazole is a promising building block for constructing conjugated polymers for high-performance non-fullerene PSCs. [Display omitted] •Difluorobenzoxadiazole-based polymers with alkylthiophene side chains were synthesized.•PffBX-2T and PffBX-TT based PSC devices showed low voltage loss of 0.54 and 0.52 V, respectively.•A high PCE up to 10.12% was achieved for PSC devices based on PffBX-TT.