Bis(naphthothiophene diimide)indacenodithiophenes as Acceptors for Organic Photovoltaics
Bis(naphthothiophene diimide)indacenodithiophenes as Acceptors for Organic Photovoltaics
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DOI：
10.1021/acs.chemmater.7b03733
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发表时间：
2017-11
影响因子：
8.6
通讯作者：
Johan Hamonnet;Masahiro Nakano;Kyohei Nakano;Hiroyoshi Sugino;K. Takimiya;K. Tajima
中科院分区：
文献类型：
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作者：
Johan Hamonnet;Masahiro Nakano;Kyohei Nakano;Hiroyoshi Sugino;K. Takimiya;K. Tajima
有机光伏（OPV）由于其独特的优势，例如轻质、机械灵活性和溶液加工性，最近受到了相当大的关注。 1−3基于富勒烯的受体在提高OPV的功率转换效率（PCE）方面发挥了重要作用；特别是，基于[6, 6]-苯基-C71-丁酸甲酯（PC71BM）和适当的π-共轭供体材料的OPV在单结太阳能电池中显示出高于11%的PCE。 4, 5 然而，富勒烯衍生物存在一些缺点，例如可见光区域吸收弱、化学稳定性差、化学结构和电子性质的可调性有限。因此，非富勒烯受体（NFA）现在正在作为一种替代方案出现。近年来，基于 NFA 的 OPV 的性能得到了迅速提高，据报道，6−9 和几种小分子 NFA 提供的 OPV 的 PCE 与具有富勒烯衍生物的最佳 OPV 相当或更高。 10− 16 在小分子NFA中，萘二酰亚胺（RyDI，图1a），17例如苝二酰亚胺（PDI）和萘二酰亚胺（NDI），由于其强电子亲和力和良好的热稳定性而被用作构建单元。 16− 23 特别是，带有基于 PDI 的小分子受体的 OPV 的 PCE 已经超过 9%。 18− 20 作为一种新型的基于RyDI的缺电子单元，我们最近报道了用于有机半导体材料的单噻吩稠合NDI，萘并[2, 3-b]噻吩二酰亚胺（NTI，图1 b）。 24, 25 NTI 单元可以通过其空的噻吩 α 位集成到具有平面 π 结构的 π 扩展系统中，从而在固态下产生红移吸收和 π− π 堆积。作为基于 NTI 的受体的模型化合物，我们将 NTI 单元与茚达并烯基 [1, 2-b: 5, 6-b'] 二噻吩 (IDT)（高级 NFA 中常用的核心单元）结合起来。 8, 9, 25− 31 在这项工作中，我们合成并表征了 NTI-IDT-NTI-三元组，即 IDT-NTI-2EH 和 IDT-NTI-1HH，32 并将它们用作 NFA（图 1 c）。与具有类似三元组结构的 NFA（PDI-IDT-PDI 三元组）相比，33 个 IDT-NTI 具有平面 π 共轭骨架（图 S1ab）。由于平面结构中有效的π共轭，IDT-NTI表现出高达780 nm的红移吸收。通过与 PBDB-T 10、34、35（图 1d）作为具有互补吸收的供体材料相结合，所得 OPV 的 PCE 高达 9%，与迄今为止报道的基于 RyDI 的 OPV 的最佳 PCE 相当。 19 方案 1 显示了 IDT-NTI 的合成。 NTI 单元 3a 和 3b 由 N,N'-未取代的 NTI (1) 制备（合成方法详见支持信息）。使用易于获得的相应醇通过Mitsunobu反应将N-取代基2-乙基己基(2EH)或1-己基庚基(1HH)引入到1的未取代的酰亚胺N-位上，得到2a和2b。随后在稠合噻吩的α位进行溴化，分别得到3a和3b。通过3a或3b与2, 7-双(三甲基甲锡烷基)-4, 4, 9, 9-四(4-己基苯基)-s-茚并基[1, 2-b: 5, 6-b']二噻吩的Stille偶联反应合成了目标化合物IDT-NTI-2EH和IDTNTI-1HH。 36 IDT-NTI-2EH 和 IDT-NTI-1HH 通过 1H 和 13C NMR、IR 和高分辨率质谱进行了全面表征（参见支持信息）。请注意，目前 IDT-NTI 的三步合成以 NTI 核心上的烷基化为特征，可以轻松地对基于 NTI 的受体进行分子修饰。 IDT-NTI 可溶于常见有机溶剂，如氯仿、
Organic photovoltaics (OPVs) have recently received considerable attention because of their unique advantages, such as lightweight, mechanical flexibility, and solutionprocessability. 1− 3 Fullerene-based acceptors have played an important role in the improvement of power conversion efficiency (PCE) of OPVs; in particular, OPVs based on [6, 6]-phenyl-C71-butyric acid methyl ester (PC71BM) and appropriate π-conjugated donor materials have shown PCEs higher than 11% in single junction solar cells. 4, 5 However, fullerene derivatives have several drawbacks, such as weak absorption in the visible region, poor chemical stability, and limited tunability of their chemical structures and electronic properties. As a consequence, nonfullerene acceptors (NFAs) is now emerging as an alternative. The performances of OPVs based on NFAs have been rapidly improved in recent years, 6− 9 and several small-molecular NFAs have been reported to afford OPVs with PCEs comparable to or higher than those of the best OPVs with fullerene derivatives. 10− 16 In the small-molecular NFAs, rylene diimide (RyDI, Figure 1 a), 17 eg, perylene diimide (PDI) and naphthalene diimide (NDI), have been employed as a building unit due to their strong electron affinity and good thermal stability. 16− 23 In particular, the PCEs of the OPVs with PDI-based smallmolecular acceptors have already exceeded 9%. 18− 20 As a novelRyDI-based electron-deficient unit, we have recently reported the monothiophene-fused NDI, naphtho [2, 3-b] thiophene diimide (NTI, Figure 1 b), for organic semiconducting materials. 24, 25 The NTI unit can be integrated via its vacant thiophene α-position into π-extended systems with planar πstructures, which gives red-shifted absorption and π− π stacking in the solid state. As a model compound for NTI-based acceptors, we combined the NTI unit with indaceno [1, 2-b: 5, 6-b′] dithiophene (IDT), a frequently used core-unit in superior NFAs. 8, 9, 25− 31 In this work, we synthesized and characterized NTI-IDT-NTI-triads, namely IDT-NTI-2EH and IDT-NTI-1HH, 32 and utilized them as NFAs (Figure 1 c). Compared to a NFA with a similar triad structure, PDI-IDT-PDI triad, 33 IDT-NTIs have a planar π-conjugated skeleton (Figure S1ab). Owing to the effective π-conjugation in the planar structures, IDT-NTIs exhibited red-shifted absorption of up to 780 nm. By combining with PBDB-T 10, 34, 35 (Figure 1 d) as a donor material with the complementary absorption, the resulting OPVs yielded promising PCEs as high as 9%, comparable to the best PCEs so far reported for RyDI-based OPVs. 19 Scheme 1 shows the synthesis of IDT-NTIs. The NTI-units, 3a and 3b, were prepared from N, N′-unsubstituted NTI (1)(the synthesis is detailed in Supporting Information). The N-substituents, 2-ethylhexyl (2EH) or 1-hexylheptyl (1HH), were introduced on the unsubstituted imide N-positions of 1 by Mitsunobu reaction using readily available corresponding alcohols to afford 2a and 2b. The following bromination at the α-position of the fused-thiophene gave 3a and 3b, respectively. The target compounds, IDT-NTI-2EH and IDTNTI-1HH, were synthesized by Stille coupling reaction of 3a or 3b with 2, 7-bis (trimethylstannyl)-4, 4, 9, 9-tetrakis (4-hexylphenyl)-s-indaceno [1, 2-b: 5, 6-b′] dithiophene. 36 IDT-NTI-2EH and IDT-NTI-1HH were fully characterized by 1H and 13C NMR, IR, and high-resolution mass spectra (see Supporting Information). Note that the present 3-step synthesis of IDT-NTIs featuring the alkylation on the NTI core enables facile molecular modifications of NTI-based acceptors. IDT-NTIs were soluble in common organic solvents, such as chloroform,