Strain and Huckel Aromaticity: Driving Forces for a Promising New Generation of Electron Acceptors in Organic Electronics
Strain and Huckel Aromaticity: Driving Forces for a Promising New Generation of Electron Acceptors in Organic Electronics
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DOI：
10.1002/anie.200905117
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发表时间：
2010-01-01
影响因子：
16.6
通讯作者：
Wudl, Fred
中科院分区：
文献类型：
--
作者：
Brunetti, F. G.;Gong, X.;Wudl, Fred
通过使用类似于印刷杂志和报纸生产中使用的辊对辊涂布机制造柔性、轻质有机光伏器件（OPV）的切实可能性使得该技术成为昂贵的晶体硅光伏电池的有效替代方案。[1-3]用于这些OPV的最广泛使用的活性层，即所谓的本体异质结（BHJ），[4，5]是基于从电子供给材料（例如光吸收和空穴传导聚合物）到电子接受组分（通常为富勒烯[60]及其衍生物1-（3-甲氧羰基）丙基-1-苯基-[6，6]-C61（[C60] PCBM））的光诱导电荷转移。[6，7]几个研究小组已经报道了广泛的新聚合物供体结构，其吸收宽波长范围内的光，并且具有窄的能隙和增加的电极处的电荷传输和收集。然而，关于不含富勒烯衍生物的受体组分的新结构的报道较少。[8-11] C60和C70 PCBM目前被认为是最成功的受体结构，尽管在修饰这些功能化富勒烯时只有轻微的改进。[12-14]例如，在[C60] PCBM的苯环上插入给电子基团以调节最低未占分子轨道（LUMO）能级，提高了开路电压（Voc），同时保持相对不变的效率。[15]此外，[C70] PCBM比[C60] PCBM吸收更宽的波长范围，[16]与低带隙聚合物如聚[2，6-（4，4-双-（2-乙基己基-4H-环戊[2，1-B; 3，4 b ']-二噻吩）-alt-4，7-（2，1，3-苯并噻二唑）]（PCPDTBT）一起使用，以拓宽光电流光谱范围。虽然获得了令人鼓舞的光电流和光电压值，但观察到由损耗机制引起的低的总体效率。[17]尽管这些富勒烯衍生物的广泛使用，新的受体的合成与当前的C60衍生物的能量水平显着不同，以及在衍生化和功能化方面的广泛的通用性是迫切需要的。在此，我们报道了基于9，9 '-联芴亚基[18]（99'BF）骨架的新一代受体化合物的内在潜力。99'BF可以被认为是四苯并富瓦烯，其原子编号反映了通过9和9'碳原子之间的双键连接的芴。在基态，由于双键的存在，99'BF被迫共面，但H1-H1'和H8-H8'质子之间的排斥相互作用扭曲了二聚体的结构。[19-21]在C9-C9'键上添加一个电子是非常有利的，这有两个主要原因：空间（“扭曲”）[22]应变消除和14-π-电子系统的芳香性增益[23]（方案1）。另一个优点是，通过电化学和ESR研究分离和表征的相应芴基团在某些条件下是稳定的。[24-26]此外，99'BF是比富勒烯更通用的支架，因为理论上，它具有12个不同的取代官能化位点。另一方面，巴克敏斯特富勒烯只能通过加成反应官能化，这导致电子结构随着每次后续加成而发生重大变化。[27基于这一推理，我们合成并表征了一系列过度拥挤的多环（方案2），并简要介绍了一些非常初步的BHJ太阳能电池。化合物6d，其被供体取代基官能化，通过将2，7，.
The tangible possibility of fabricating flexible, lightweight organic photovoltaic devices (OPVs) by using roll-to-roll coaters, similar to those used in the production of print magazines and newspapers, renders this technology a valid alternative to expensive crystalline silicon photovoltaic cells.[1–3] The most widely used active layer for these OPVs, the so-called bulk heterojunction (BHJ),[4, 5] is based on photoinduced charge transfer from an electron-donating material, such as a light-absorbing and hole-conducting polymer, to an electron-accepting component, typically fullerene [60] and its derivative 1-(3-methoxycarbonyl) propyl-1-phenyl-[6, 6]-C61 ([C60] PCBM).[6, 7] Several research groups have reported a wide range of new polymeric donor structures that absorb light over a broad wavelength range, and have a narrow energy gap and increased charge transport and collection at the electrode. However, there have been fewer reports on new structures of acceptor components that do not contain fullerene derivatives.[8–11] C60 and C70 PCBMs are currently considered the most successful acceptor architectures, despite only slight improvements when modifying these functionalized fullerenes.[12–14] For example, the insertion of electron-donating groups on the phenyl ring of the [C60] PCBM to tune the lowest unoccupied molecular orbital (LUMO) energy levels improved the open-circuit voltage (Voc), while maintaining a relatively unchanged efficiency.[15] Furthermore,[C70] PCBM, which absorbs a wider range of wavelengths than [C60] PCBM,[16] was employed with low-band-gap polymers such as poly [2, 6-(4, 4-bis-(2-ethylhexyl-4H-cyclopenta [2, 1-b; 3, 4b’]-dithiophene)-alt-4, 7-(2, 1, 3-benzothiadizole)](PCPDTBT), to broaden the photocurrent spectral range. Although encouraging photocurrent and photovoltage values were obtained, a low overall efficiency, which arises from loss mechanisms, was observed.[17] Despite the wide use of these fullerene derivatives, the synthesis of new acceptors with energy levels significantly different from those of current C60 derivatives, and wide versatility in terms of derivatization and functionalization is urgently required. Herein, we report the inherent potential of a new generation of acceptor compounds based on the 9, 9’-bifluorenylidene [18](99’BF) backbone. 99’BF could be considered a tetrabenzofulvalene with an atom numbering that reflects fluorene linked by a double bond between the 9 and 9’carbon atoms. In the ground state, 99’BF is forced to be coplanar because of the presence of the double bond, but the repulsive interaction between the H1–H1’and H8–H8’protons twists the structure of the dimer.[19–21] The addition of one electron across the C9–C9’bond is highly favorable for two main reasons: steric (“twist”)[22] strain relief and gain in aromaticity to a 14-π-electron system [23](Scheme 1).A further advantage is that the corresponding fluorene radical, which was isolated and characterized by electrochemical and ESR studies, is stable under certain conditions.[24–26] In addition, 99’BF is a much more versatile scaffold than the fullerenes as, theoretically, it has twelve different sites for functionalization by substitution. On the other hand, buckminsterfullerene can only be functionalized by addition reactions, which result in a major modification of the electronic structure with each subsequent addition.[27, 28] Based on this reasoning, we synthesized and characterized a series of overcrowded polycycles (Scheme 2), and some very preliminary BHJ solar cells are briefly presented. Compound 6d, which was functionalized with donor substituents, was obtained from a one-pot reaction by treating 2, 7 …