Regio-asymmetric polymers based on fluorinated benzothiadiazole-benzodithiophene for polymer solar cells with a high open-circuit voltage

• Published in: New journal of chemistry Vol. 43; no. 9; pp. 381 - 389
• Main Authors: Li, Zhanfeng, Liu, Caijun, Gan, Guoyue, Sun, Na, Li, Xueqiao, Tong, Yahui, Wang, Hua, Hao, Yuying
• Format: Journal Article
• Language: English
• Published: CAMBRIDGE Royal Soc Chemistry 25.02.2019; Royal Society of Chemistry
• Subjects: Asymmetry; Backbone; Chemistry; Chemistry, Multidisciplinary; Current carriers; Energy conversion efficiency; Energy levels; Fluorination; Heterojunction devices; Open circuit voltage; Optoelectronics; Photovoltaic cells; Physical Sciences; Polymers; Science & Technology; Solar cells; ELECTRON-RICH UNIT; SMALL-MOLECULE; PERFORMANCE; CONJUGATED POLYMER; COPOLYMERS; EFFICIENT; THIOPHENE; MORPHOLOGY; ACCEPTOR
• ISSN: 1144-0546; 1369-9261
• DOI: 10.1039/c9nj00001a

Two regio-asymmetric polymers PR2F and PR1F with three repeat units A-D-A, π-D-A, and π-D-π along the polymer backbone were obtained by polymerizing different fluorinated benzothiadiazole-thiophene units, FBT-T and 2FBT-T units (A-π), with a benzodithiophene unit (D), respectively. Here, the new regio-asymmetric polymers were different from traditional polymers featuring a D-A or D-π-A-π backbone. Both the regio-asymmetric polymers showed a low lying HOMO energy level in relation to that of the PC 61 BM acceptor and then a high open-circuit voltage of ∼1 V was observed in both PR2F and PR1F devices. Bulk-heterojunction devices based on PR2F with difluorinated BT exhibited an appreciable power conversion efficiency (PCE) of 4.73% due to the relatively high and balanced charge carrier mobilities, while the mono-fluorinated BT polymer PR1F -based devices showed a lower PCE of 2.92%. These results indicate that the regio-asymmetric conjugated polymers are a promising class of materials for polymer solar cell applications, and it is significant to further understand the influence of the polymer structure on the optoelectronic properties. Regio-asymmetric polymer PR2F -based devices with SVA exhibited an appreciable PCE of 4.73% with a high V OC of 0.98 V.