The effect of alkylthio substituents on the photovoltaic properties of conjugated polymers

• Published in: Organic electronics Vol. 68; pp. 50 - 55
• Main Authors: Li, Yi, Zhong, Yuancong, Jiang, Huanxiang, Rath, Thomas, Wang, Qian, Ehmann, Heike M.A., Trimmel, Gregor, Wen, Shuguang, Zhang, Yong, Yang, Renqiang
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.05.2019
• Subjects: Alkylthio side chain; Conjugated polymer; Non-covalent interaction; Polymer solar cells; Power conversion efficiency; Conjugated polymer; Non-covalent interaction; Alkylthio side chain; Power conversion efficiency; Polymer solar cells
• ISSN: 1566-1199; 1878-5530
• DOI: 10.1016/j.orgel.2019.01.051

Alkylthio groups are effectively utilized in molecule design to improve the performance of polymer solar cells (PSCs). In this study, two conjugated polymers, P1 and P2, were designed and synthesized with alkyl and alkylthio side chains substituted on thiophene as π bridges, respectively. Owing to the twist of the backbone induced by the steric hindrance of the hexyl side chains, polymer P1 shows a low power conversion efficiency (PCE) of 2.83% in PSC devices with PC71BM as acceptor and a low hole mobility of 1.85 × 10−5 cm2 V−1 s−1 in the blend film. In contrast to the steric hindrance of the alkyl side chain, the alkylthio side chain can form S⋯S non-covalent interaction with an adjacent thiophene to maintain the molecular planarity and strengthen intermolecular interaction, which is designed in polymer P2 to improve the photovoltaic performance. As a result, the P2-based devices exhibit a higher PCE of 6.15% with an open-circuit voltage (VOC) of 0.71 V, a short-circuit current (JSC) of 14.55 mA cm−2 and a fill factor (FF) of 59.5%. The hole mobility is also increased to 2.20 × 10−4 cm2 V−1 s−1. Our results demonstrate that introducing S⋯S non-covalent interaction into conjugated polymers could be a useful strategy for building high performance photovoltaic materials. [Display omitted] •Two conjugated polymers P1 and P2 with alkyl and alkylthio side chains on thiophene as π bridges were synthesized.•P2 showed higher hole mobility and stronger intermolecular interaction due to forming S…S non-covalent interaction.•The optimized P2 based device exhibited higher PCE of 6.15% than P1.