Non-fullerene electron acceptors for use in organic solar cells.
Non-fullerene electron acceptors for use in organic solar cells.
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用于有机太阳能电池中的非富烯电子受体。
DOI：
10.1021/acs.accounts.5b00199
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发表时间：
2015-11-17
影响因子：
18.3
通讯作者：
McCulloch I
中科院分区：
文献类型：
--
作者：
Nielsen CB;Holliday S;Chen HY;Cryer SJ;McCulloch I
溶液处理的有机光伏器件中的活性层包含光吸收电子供体半导体（通常为聚合物）和电子接受富勒烯受体。尽管已经有大量的努力来优化供体材料的吸收，能量和传输特性，但富勒烯仍然是所有高性能器件中的唯一电子受体。最近，一些新的非富勒烯受体已被证明在比较器件中优于富勒烯。这个帐户描述了这一进展，讨论分子设计的考虑因素和正在出现的结构-性能关系。取代富勒烯受体的动机源于它们的合成可结晶性，导致操纵前沿能级的限制，以及在太阳光谱范围内的吸收差，以及经历制造后结晶的固有趋势，导致器件不稳定。新的受体必须解决这些限制，提供具有高消光系数的可调吸收，从而有助于器件光电流。改变和优化特定供体聚合物的最低未占分子轨道（LUMO）能级的能力也是一个重要的要求，确保电子转移的能量损失最小和尽可能高的内部电压。最初，评价二萘嵌苯二酰亚胺受体作为有前途的受体材料。这些缺电子芳族分子可以表现出良好的电子传输，促进了紧密堆积的人字形晶体图案，并且它们的能级可以合成调谐。这类材料的主要缺点，它们倾向于结晶在太大的长度尺度上的最佳异质结纳米结构，已被证明是克服通过引入构象扭曲通过空间效应。这主要是通过将两个单元耦合在一起，形成具有大的分子内扭曲的二聚体来实现的，这抑制了成核和晶体生长。具有扩展π轨道离域的旋转对称芳香族小分子的通用设计概念，包括多环芳烃、酞菁等，也提供了一些优良的小分子受体。在大多数情况下，可以引入额外的吸电子官能度，例如酰亚胺或酯基，以稳定LUMO并改善性能。已经开发了新的棒状受体，其中富电子和贫电子片段的分子轨道杂化可以明智地用于精确控制能级。构象和分子间缔合可以通过外围官能化来控制，从而优化结晶长度尺度。特别是，使用绕丹宁端基，通过短的桥接芳族链电子耦合，已经是一个成功的策略，具有有前途的设备效率归因于高的LUMO能级和随后的大的开路电压。
The active layer in a solution processed organic photovoltaic device comprises a light absorbing electron donor semiconductor, typically a polymer, and an electron accepting fullerene acceptor. Although there has been huge effort targeted to optimize the absorbing, energetic, and transport properties of the donor material, fullerenes remain as the exclusive electron acceptor in all high performance devices. Very recently, some new non-fullerene acceptors have been demonstrated to outperform fullerenes in comparative devices. This Account describes this progress, discussing molecular design considerations and the structure–property relationships that are emerging. The motivation to replace fullerene acceptors stems from their synthetic inflexibility, leading to constraints in manipulating frontier energy levels, as well as poor absorption in the solar spectrum range, and an inherent tendency to undergo postfabrication crystallization, resulting in device instability. New acceptors have to address these limitations, providing tunable absorption with high extinction coefficients, thus contributing to device photocurrent. The ability to vary and optimize the lowest unoccupied molecular orbital (LUMO) energy level for a specific donor polymer is also an important requirement, ensuring minimal energy loss on electron transfer and as high an internal voltage as possible. Initially perylene diimide acceptors were evaluated as promising acceptor materials. These electron deficient aromatic molecules can exhibit good electron transport, facilitated by close packed herringbone crystal motifs, and their energy levels can be synthetically tuned. The principal drawback of this class of materials, their tendency to crystallize on too large a length scale for an optimal heterojunction nanostructure, has been shown to be overcome through introduction of conformation twisting through steric effects. This has been primarily achieved by coupling two units together, forming dimers with a large intramolecular twist, which suppresses both nucleation and crystal growth. The generic design concept of rotationally symmetrical aromatic small molecules with extended π orbital delocalization, including polyaromatic hydrocarbons, phthalocyanines, etc., has also provided some excellent small molecule acceptors. In most cases, additional electron withdrawing functionality, such as imide or ester groups, can be incorporated to stabilize the LUMO and improve properties. New calamitic acceptors have been developed, where molecular orbital hybridization of electron rich and poor segments can be judiciously employed to precisely control energy levels. Conformation and intermolecular associations can be controlled by peripheral functionalization leading to optimization of crystallization length scales. In particular, the use of rhodanine end groups, coupled electronically through short bridged aromatic chains, has been a successful strategy, with promising device efficiencies attributed to high lying LUMO energy levels and subsequently large open circuit voltages.