Materials Design Considerations for Charge Generation in Organic Solar Cells
Materials Design Considerations for Charge Generation in Organic Solar Cells
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DOI：
10.1021/cm402403z
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发表时间：
2014-01-14
影响因子：
8.6
通讯作者：
Durrant, James R.
中科院分区：
文献类型：
--
作者：
Dimitrov, Stoichko D.;Durrant, James R.
本文综述了我们在体-异质结有机太阳能电池光生电荷材料设计指南方面的一些最新进展。在过去的7年里，我们的团队使用瞬时吸收测量来确定300多种不同有机给体/受体共混膜的长寿命极化子对的相对量子产率。我们已经证明，这种电荷分离的光学分析可以作为完整器件中光电流产生效率的一个强有力的指示器。在这篇综述中，我们考虑了从这些研究中可以得到的教训，这些研究涉及到决定这种太阳能电池中这种光致电荷分离效率的参数。通过对几种材料系列的研究，我们一致地发现，能量偏移驱动电荷分离是这种电荷产生效率的关键决定因素，从而决定了光电流产生的效率。此外，我们发现，驱动电荷分离所需的能量偏移量的大小，以及这种能量依赖的强度，在不同的材料类别之间有很大的差异。特别是，研究发现，以二酮基吡咯和噻唑并噻唑为基础的聚合物等共聚物能够以比P3HT等聚噻吩类化合物低得多的能量偏移量驱动PCBM共混物中的电荷分离，同时还观察到用更结晶性的二茂铁二亚胺受体取代PCBM以降低电荷分离的能量偏移量要求。我们进一步讨论了薄膜微结构在决定电荷分离效率中的作用，包括混合区和纯区的作用，PCBM激子扩散限制，以及材料结晶度在调制材料能级中的作用，从而提供了可以稳定电荷空间分离的额外能量偏移量。考虑的其他因素包括库仑束缚极化子对或电荷转移态的作用、器件电场、载流子迁移率、三重态激子和光子能量。我们简要地讨论了一个与这些和其他观测结果一致的电荷分离模型。最后，我们总结了从这些研究中可以得出的高效电荷光生的材料设计指南。
This article reviews some of our recent progress on materials design guidelines for photoinduced charge generation in bulk-heterojunction organic solar cells. Over the last 7 years, our group has employed transient absorption measurement to determine the relative quantum yields of long-lived polaron pairs for over 300 different organic Donor/Acceptor blend films. We have shown that this optical assay of charge separation can be a strong indicator of photocurrent generation efficiency in complete devices. In this review, we consider the lessons that can be drawn from these studies concerning the parameters that determine efficiency of this photoinduced charge separation in such solar cells. We consistently find, from studies of several materials series, that the energy offset driving charge separation is a key determinant of the efficiency of this charge generation, and thereby photocurrent generation. Moreover, we find that the magnitude of the energy offset required to drive charge separation, and the strength of this energetic dependence, varies substantially between materials classes. In particular, copolymers such as diketopyrrolopyrrole- and thiazolothiazole-based polymers are found to be capable of driving charge separation in blends with PCBM at much lower energy offsets than polythiophenes, such as P3HT, while replacement of PCBM with more crystalline perylene diimide acceptors is also observed to reduce the energy offset requirement for charge separation. We go on to discuss the role of film microstructure in also determining the efficiency of charge separation, including the role of mixed and pure domains, PCBM exciton diffusion limitations and the role of material crystallinity in modulating material energetics, thereby providing additional energy offsets that can stabilize the spatial separation of charges. Other factors considered include the role of Coulombically bound polaron pair or charge transfer states, device electric fields, charge carrier mobilities, triplet excitons, and photon energy. We discuss briefly a model for charge separation consistent with these and other observations. We conclude by summarizing the materials design guidelines for efficient charge photogeneration that can be drawn from these studies.