Using Electronic Sum-Frequency Generation to Analyze the Interfacial Structure of Singlet Fission-Capable Perylenediimide Thin Films
Using Electronic Sum-Frequency Generation to Analyze the Interfacial Structure of Singlet Fission-Capable Perylenediimide Thin Films
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DOI：
10.1021/acs.jpcc.0c01025
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发表时间：
2020-05-28
影响因子：
3.7
通讯作者：
Roberts, Sean T.
中科院分区：
文献类型：
--
作者：
Cotton, Daniel E.;Moon, Aaron P.;Roberts, Sean T.
经历单重态激子裂变的有机材料通过将高能光子转换成成对的自旋三重态激子而显示出作为用于半导体太阳能电池的激子倍增材料的前景。然而，由于从有机光吸收层到半导体能量受体（例如体硅）的三重态转移效率低下，基于单重态裂变的太阳能电池经历了延迟实施。由于三重态转移需要三重态激发的有机分子和半导体能量受体之间的轨道重叠，因此转移将由连接这些材料的界面的结构决定。合理的设计和控制的转移需要详细的信息，这种埋界面的结构和能量环境，这是很难探测实验。为此，电子和频发生（ESFG），一种非侵入性的光谱学，可以通过提供有关有机半导体结的分子顺序和电子结构的界面选择性信息来满足这一需求。在这里，我们证明了ESFG的潜力，通过比较掩埋的界面结构的两个单线态裂变能力的perylenediimide衍生物沉积在玻璃上的薄膜。我们发现ESFG光谱信号的带隙的每个perylenedimide衍生物在玻璃界面相对于他们的散装，我们表明是一致的亚埃的变化在埋界面的分子间包装的显着收窄。此外，测量的ESFG光谱的偏振依赖性的分析表明，每个衍生物采用不同的取向，他们的二萘嵌苯核心相对于衬底，这具有重要的后果，实现激子转移跨越三重态提取半导体结。
Organic materials that undergo singlet exciton fission show promise as exciton multiplication materials for semiconductor solar cells by converting high-energy photons into pairs of spin-triplet excitons. However, singlet fission-based solar cells have experienced delayed implementation due to inefficient triplet transfer from organic light-absorbing layers to semiconductor energy acceptors, such as bulk silicon. As triplet transfer requires orbital overlap between the triplet-excited organic molecule and semiconductor energy acceptor, transfer will be dictated by the structure of the interface connecting these materials. Rational design and control of transfer requires detailed information about the structural and energetic environment of this buried interface, which is difficult to probe experimentally. To this end, electronic sum-frequency generation (ESFG), a noninvasive spectroscopy, can address this need by providing interface-selective information about both the molecular order and electronic structure of organic:semiconductor junctions. Here, we demonstrate ESFG's potential by comparing the buried interfacial structure of two singlet fission-capable perylenediimide derivatives deposited as thin films on glass. We find ESFG spectra signal a prominent narrowing of the bandgap of each perylenediimide derivative at the glass interface relative to their bulk, which we show is consistent with a subangstrom change in intermolecular packing at the buried interface. In addition, analysis of the polarization dependence of measured ESFG spectra shows that each derivative adopts different orientations of their perylene cores with respect to the substrate, which has important consequences for achieving exciton transfer across triplet-extracting semiconductor junctions.