Domain Compositions and Fullerene Aggregation Govern Charge Photogeneration in Polymer/Fullerene Solar Cells
Domain Compositions and Fullerene Aggregation Govern Charge Photogeneration in Polymer/Fullerene Solar Cells
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DOI：
10.1002/aenm.201400116
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发表时间：
2014-08-05
影响因子：
27.8
通讯作者：
Gomez, Enrique D.
中科院分区：
文献类型：
--
作者：
Kesava, Sameer Vajjala;Fei, Zhuping;Gomez, Enrique D.
有机半导体混合物的复杂微结构继续模糊活性层形态和光伏器件性能之间的联系。例如，聚合物/富勒烯太阳能电池的活性层中混合相的普遍存在产生了多个形态上不同的界面，这些界面能够进行激子解离或电荷复合。在这里，它表明，域组合物和富勒烯聚集可以强烈地调制在超快的时间尺度的电荷光生通过研究的模型系统，低带隙聚合物，聚[（4，4 '-双（2-乙基己基）二噻吩并[3，2-B：2'，3 '-d] germole）-2，6-二基-alt-（2，1，3-苯并噻唑-二唑）-4，7-二基]，和[6，6] w-苯基-C-71-丁酸甲酯的混合物。使用能量过滤透射电子显微镜（EFTEM）和共振软X射线散射的结构表征显示出类似的微观结构，即使在整体膜组合物的变化。然而，从EFTEM生成的组合物地图表明，混合域的组合物与整体膜组合物的变化显着。此外，混合域中的聚合物的量与器件性能呈负相关。使用超快红外光谱的光致吸收研究表明，极化子浓度最高时，混合域包含最少的聚合物。掠入射X射线散射结果表明，较大的富勒烯相干长度与较高的极化子产额。因此，混合域的纯度对于有效的电荷光生至关重要，因为纯度调节富勒烯聚集和电子离域。
The complex microstructure of organic semiconductor mixtures continues to obscure the connection between the active layer morphology and photovoltaic device performance. For example, the ubiquitous presence of mixed phases in the active layer of polymer/fullerene solar cells creates multiple morphologically distinct interfaces which are capable of exciton dissociation or charge recombination. Here, it is shown that domain compositions and fullerene aggregation can strongly modulate charge photogeneration at ultrafast timescales through studies of a model system, mixtures of a low band-gap polymer, poly[(4,4'-bis(2-ethylhexyl) dithieno[3,2-b:2',3'-d] germole)-2,6-diyl-alt-(2,1,3-benzothia-diazole)-4,7-diyl], and [6,6]w-phenyl-C-71-butyric acid methyl ester. Structural characterization using energyfiltered transmission electron microscopy (EFTEM) and resonant soft X-ray scattering shows similar microstructures even with changes in the overall film composition. Composition maps generated from EFTEM, however, demonstrate that compositions of mixed domains vary significantly with overall film composition. Furthermore, the amount of polymer in the mixed domains is inversely correlated with device performance. Photoinduced absorption studies using ultrafast infrared spectroscopy demonstrate that polaron concentrations are highest when mixed domains contain the least polymer. Grazing-incidence X-ray scattering results show that larger fullerene coherence lengths are correlated to higher polaron yields. Thus, the purity of the mixed domains is critical for efficient charge photogeneration because purity modulates fullerene aggregation and electron delocalization.