Diindenoperylene derivatives: A model to investigate the path from molecular structure via morphology to solar cell performance
Diindenoperylene derivatives: A model to investigate the path from molecular structure via morphology to solar cell performance
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DOI：
10.1016/j.orgel.2013.04.006
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发表时间：
2013-07
影响因子：
3.2
通讯作者：
C. Schuenemann;A. Petrich;R. Schulze;D. Wynands;J. Meiss;M. Hein;J. Jankowski;C. Elschner;Joerg Alex;M. Hummert;K. Eichhorn;K. Leo;M. Riede
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文献类型：
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作者：
C. Schuenemann;A. Petrich;R. Schulze;D. Wynands;J. Meiss;M. Hein;J. Jankowski;C. Elschner;Joerg Alex;M. Hummert;K. Eichhorn;K. Leo;M. Riede
有效的有机电子器件需要对分子结构、薄膜生长和器件性能之间的关系有详细的了解，目前这只是部分了解。在这里，我们表明，供体吸收材料的分子结构的微小变化导致有机太阳能电池内的分子间排列的显着变化。为此目的，苯环和丙基侧链稠合到二茚并萘嵌苯（DIP）分子。掠入射X射线衍射和可变角椭圆偏振光谱是一个强大的组合，以获得有关薄膜生长的详细信息。制备了以C_（60）为受体、DIP衍生物为给体的平面和体异质结太阳能电池，研究了薄膜形貌对器件性能的影响。由于其平面结构，DIP被发现是高度结晶的原始和DIP：C60共混物膜，而其衍生物生长液晶。这表明苯环引起的空间位阻强烈干扰了分子排列。在DIP衍生物的平面异质结太阳能电池中大于75%的高填充因子（FF）表明在原始的类液晶结晶吸收层中优异的电荷传输。然而，这些材料的体异质结令人惊讶地导致仅54%的低FF，这是由弱相分离引起的，并且因此由于较低有序的薄膜生长而导致不良的电荷载流子渗透路径。相比之下，晶体DIP：C60异质结导致高达65%的高FF，因为晶体生长诱导电荷载流子的更好的渗透。然而，这种晶体生长模式的主要缺点是DIP分子在原始膜和共混膜中的几乎直立的取向。这种排列导致低吸收，因此光电流显著低于DIP衍生物器件，其中类液晶晶体生长导致更水平的分子排列。我们的研究结果强调了有机半导体器件中分子结构与器件性能关系的复杂性。
Efficient organic electronic devices require a detailed understanding of the relation between molecular structure, thin film growth, and device performance, which is only partially understood at present. Here, we show that small changes in molecular structure of a donor absorber material lead to significant changes in the intermolecular arrangement within organic solar cells. For this purpose, phenyl rings and propyl side chains are fused to the diindenoperylene (DIP) molecule. Grazing incidence X-ray diffraction and variable angle spectroscopic ellipsometry turned out to be a powerful combination to gain detailed information about the thin film growth. Planar and bulk heterojunction solar cells with C60 as acceptor and the DIP derivatives as donor are fabricated to investigate the influence of film morphology on the device performance. Due to its planar structure, DIP is found to be highly crystalline in pristine and DIP:C60 blend films while its derivatives grow liquid-like crystalline. This indicates that the molecular arrangement is strongly disturbed by the steric hindrance induced by the phenyl rings. The high fill factor (FF) of more than 75% in planar heterojunction solar cells of the DIP derivatives indicates excellent charge transport in the pristine liquid-like crystalline absorber layers. However, bulk heterojunctions of these materials surprisingly result in a low FF of only 54% caused by a weak phase separation and thus poor charge carrier percolation paths due to the lower ordered thin film growth. In contrast, crystalline DIP:C60 heterojunctions lead to high FF of up to 65% as the crystalline growth induces better percolation for the charge carriers. However, the major drawback of this crystalline growth mode is the nearly upright standing orientation of the DIP molecules in both pristine and blend films. This arrangement results in low absorption and thus a photocurrent which is significantly lower than in the DIP derivative devices, where the liquid-like crystalline growth leads to a more horizontal molecular alignment. Our results underline the complexity of the molecular structure-device performance relation in organic semiconductor devices.