Improving photovoltaic performance of benzothiadiazole-based small molecules: A synergistic effect of non-covalent inter
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Improving photovoltaic performance of benzothiadiazole-based small molecules: A synergistic effect of non-covalent interaction and aryl terminal group Qian Liu, Jiyong Denga), Dong Yan, Xianwei Huang, Yunfeng Liao, Qiang Taob) Hunan Provincial Key Laboratory of Environmental Catalysis & Waste Recycling, School of Materials and Chemical Engineering, Hunan Institute of Engineering, Xiangtan 411104, China a) Address all correspondence to these authors. e-mail: [email protected] b) e-mail: [email protected] Received: 25 March 2020; accepted: 28 August 2020
A–Ar–A-type small molecule (SM) of Py-2DTOBT and Py-2DTOBTPh with an Ar(A–D)2 framework were synthesized, in which 2,7-pyrene (Py) and alkoxyl-substituted benzothiadiazole (OBT) were, respectively, used as the central aryl (Ar) and arm acceptor (A), while 3-phenanthrene (Ph) was used as a terminal donor (D) in Py-2DTOBTPh. By comparison with the parent SM of Py-2DTBT, where 2,7-pyrene (Py) and benzothiadiazole (BT) were used as the central aryl (Ar) and arm acceptor (A), the effects of non-covalent interactions and the terminal group on optical, electrochemical, and photovoltaic properties were investigated. The gradually improved photovoltaic performances were observed among Py-2DTBT, Py-2DTOBT, and Py-2DTOBTPh based organic solar cells. A power conversion efficiency (PCE) of 2.83% was obtained in the Py-2DTOBTPh/PC71BM-based device, which is a 53% improvement related to that of Py-2DTOBT and three times enhanced related to that of Py-2DTBT(Py-2DTOBT:PCE of 1.86%, Py-2DTBT:PCE of 0.74%).
Introduction Extensive efforts have been made in materials and physical fundamentals to develop high performance organic solar cells (OSCs) over the last two decades [1, 2, 3, 4, 5]. OSCs based on the bulk heterojunction (BHJ) structure with electron donating and accepting materials have afforded high power conversion efficiencies (PCEs) over 15% [6, 7, 8]. Organic small molecules (SMs) have been widely investigated as functional active layer materials in OSCs due to their unique characters of well-defined structures, good dispersity, easy purification, and superior batch-to-batch reproducibility compared with the polymer counterparts [9, 10, 11, 12, 13, 14]. However, there are some drawbacks, for instance, to achieve a high-quality thin film from a solution can be trickier when using SMs instead of polymers. Non-covalent interactions are defined as contact distances between two atoms, which are shorter than the sum of the van der Waals radii of the two corresponding atoms [15, 16, 17]. Non-covalent heteroatom/weak hydrogen bonding
interactions normally offer some advantages, such as planarization and strong interchain packing in the bulk material [18]. For instance, Huang et al. reported small molecular acceptor IDT-Tz by employing the thiazole unit as the π-bridge [19]. The IDT-Tz demonstrated reduced reorganization energy, increased charge transport mobility, and enhanced photovoltaic performance, as introduction N-S non-covalent conformational locks enhanced the rigidity and p
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