Department of Physics and Institute of Advanced Materials, Hong Kong Baptist University, Kowloon Tong, Hong Kong SAR, P. R. China.
Department of Chemistry, Energy Institute and Hong Kong Branch of Chinese National, Engineering Research Center for Tissue Restoration and Reconstruction, Hong Kong University of Science and Technology (HKUST), Clear Water Bay, Kowloon, Hong Kong.
Adv Mater. 2019 Nov;31(44):e1903998. doi: 10.1002/adma.201903998. Epub 2019 Sep 18.
Conventional organic solar cell (OSC) systems have significant energy offsets between the donor and acceptor both at the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels. Because of this, in a bulk heterojunction (BHJ) system, electrons typically transport in acceptors, whereas holes typically transport in donors. It is not favorable for electrons to hop back and forth between the donor and acceptor because the hopping is energetically disfavored. In such conventional OSC systems, the addition of donor polymer to acceptor films should typically reduce the electron mobility. In this study, a surprisingly large increase (up to 30×) in electron mobility is observed in an OSC blend when introducing a polymer donor into small molecular acceptor. By ruling out morphology reasons, it is shown that the donor polymer can assist the electron transport by providing "bridges" or a "shortcut" for electron transport across the domains of small molecular acceptors. This can happen because, for these systems, the LUMO offset is small. The study shows the benefits of donor-assisted electron transport in BHJ systems with small energetic offsets. This finding could be also applied to other fields to tune the optimized charge transport property of organic materials or slush blends.
传统的有机太阳能电池 (OSC) 体系在供体和受体的最高占据分子轨道 (HOMO) 和最低未占据分子轨道 (LUMO) 能级之间存在显著的能量偏移。因此，在体异质结 (BHJ) 体系中，电子通常在受体中传输，而空穴通常在供体中传输。电子在供体和受体之间来回跳跃是不利的，因为跳跃在能量上是不利的。在这种传统的 OSC 体系中，向受体薄膜中添加供体聚合物通常会降低电子迁移率。在这项研究中，当向小分子受体中引入聚合物供体时，在 OSC 混合物中观察到电子迁移率惊人地增加（高达 30 倍）。通过排除形貌原因，表明供体聚合物可以通过为电子在小分子受体的域之间的传输提供“桥梁”或“捷径”来辅助电子传输。这可能是因为对于这些体系，LUMO 偏移较小。该研究表明，在具有小能量偏移的 BHJ 体系中，施主辅助电子输运具有优势。这一发现也可以应用于其他领域，以调整有机材料或泥浆混合物的优化电荷传输性能。
