Identifying Molecular Orientation in a Bulk Heterojunction Film by Infrared Reflection Absorption Spectroscopy
Identifying Molecular Orientation in a Bulk Heterojunction Film by Infrared Reflection Absorption Spectroscopy
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DOI：
10.1021/acsomega.8b00099
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发表时间：
2018-05-01
期刊：
影响因子：
4.1
通讯作者：
Taima, Tetsuya
中科院分区：
文献类型：
--
作者：
Chikamatsu, Tatsuki;Shahiduzzaman, Md;Taima, Tetsuya
在碘化铜（CuI）衬底上的单组分膜中，酞菁锌（ZnPc）有机分子的分子取向可以通过ZnPc分子与CuI之间的pi-d轨道相互作用来控制，从而实现分子取向平躺在衬底上（平on）。通过在ZnPc：富勒烯（C60）体异质结（BHJ）薄膜和衬底之间引入CuI中间层，有机光伏电池的性能提高了3倍。然而，支撑太阳能电池性能增强的机制尚不清楚。本文报道了在不同衬底上真空沉积共蒸发ZnPc:C60 BHJ薄膜的原位反射吸收光谱测量结果，以研究ZnPc的分子取向。我们的研究结果表明，通过BHJ薄膜与衬底之间的强p-p相互作用，可以成功地识别出ZnPc分子在CuI夹层和ZnPc衬底上的ZnPc:C60 BHJ薄膜中的平面分子取向。在共蒸发ZnPc:C60薄膜中，单个ZnPc分子之间的p-p相互作用强于ZnPc分子与CuI之间的pi-d相互作用，这一点从原位反射吸收光谱测定的ZnPc分子取向中可以看出。我们的研究结果表明，精确控制薄膜的分子取向可以提高有机光伏（OPV）的性能。目前的工作提供了重要的见解，将使更高性能的OPV电池的设计。
The molecular orientation of organic molecules of zinc phthalocyanine (ZnPc) in single-component films on copper iodide (CuI) substrates can be controlled to achieve a molecular orientation lying flat on the substrate (flat-on) owing to pi-d orbital interactions between the ZnPc molecules and the CuI. A 3-fold enhancement in the performance of organic photovoltaic cells has been reported by introducing a CuI interlayer between a ZnPc:fullerene (C60) bulk heterojunction (BHJ) film and the substrate. However, the mechanism underpinning the resultant solar cell performance enhancement was unclear. Herein, we report on the results of using in situ reflection absorption spectroscopy measurements during the vacuum deposition of coevaporated ZnPc:C60 BHJ films on various substrates to investigate the ZnPc molecular orientation. Our results revealed that the flat-on molecular orientation of ZnPc molecules in ZnPc:C60 BHJ films on CuI interlayers and flat-on ZnPc substrates can be successfully identified via the strong p-p interactions between the BHJ film and the substrate. The p-p interactions between individual ZnPc molecules are stronger than the pi-d interactions between ZnPc molecules and CuI in coevaporated ZnPc:C60 films, as is evident from the molecular orientation of ZnPc, as determined by in situ reflection absorption spectroscopy. Our findings demonstrate that precisely controlling the molecular orientations of the films could enhance organic photovoltaic (OPV) performance. The present work provides important insights that will enable the design of higher performance OPV cells.