Controlling Morphology in Polymer–Fullerene Mixtures
Controlling Morphology in Polymer–Fullerene Mixtures
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DOI：
10.1002/adma.200701519
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发表时间：
2008-01
影响因子：
29.4
通讯作者：
A. Moulé;K. Meerholz
中科院分区：
文献类型：
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作者：
A. Moulé;K. Meerholz
在过去的几年中，聚合物-富勒烯混合物已经被深入研究用于有机太阳能电池，因为它们可以从溶液中沉积，与低成本的卷到卷制造技术兼容，并且已经显示出高达4- 5%的高功率转换效率（g）。最好的器件由单个体异质结有源层组成，其中聚合物（供体）和富勒烯（受体）从共同的溶剂中沉积。当溶剂干燥时，供体和受体组分分离成域。太阳能电池的最终效率已被证明对所形成的域的尺寸、组成和结晶度极其敏感。通过热处理技术和长时间溶剂固化，用[6，6]-苯基C61-丁酸甲酯（PCBM）和区域规整聚（3-己基噻吩）（P3 HT）的混合物制造的器件的形态得到改善，从而获得创纪录的效率。最近，已经引入了一种用于增加P3 HT组分的结晶度的方法，该方法包括将P3 HT的预成形纳米纤维从溶液中过滤出来，并将制备的纳米分散体与PCBM混合以增加铸态器件的效率。有趣的是，通过将低分子量（MW）无定形P3 HT混合回溶液中以减少有源层的结晶含量，从而增加结晶域之间的连接，实现了最佳的器件性能。MW对P3 HT/PCBM太阳能电池影响的研究表明，大的多分散性和超过19000 g mol-1的数均分子量（Mn）导致效率提高。有机场效应晶体管（OFET）器件的形态学研究表明，增加MW导致更好的网络形成之间的结晶域。使用透射电子显微镜（TEM），掠射角X射线衍射（XRD），原子力显微镜（AFM），扫描电子显微镜（SEM），核磁共振，和各种其他的光学和电学技术，这些改进的设备的形态进行了研究。形态学研究给出了其中P3 HT形成对准/结晶域的装置的图片，在所述对准/结晶域之间是P3 HT和PCBM的无定形段。这些域形成较大的尺寸和结晶度较高的热处理温度和较长的溶剂浸泡时间。根据制造和测量技术，P3 HT的对齐域被描绘为纤维或不成形的团块。然而，这些研究中的大多数不允许量化最终器械中聚结/结晶的P3 HT的百分比。只有通过使用反渗透过滤技术，作者才有能力控制溶液和最终装置中P3 HT的结晶含量。该技术的缺点是需要更复杂的制备，并且过滤的P3 HT被限制为纤维形式，其需要添加无定形P3 HT以提供结晶域之间的连接。我们在这里提出了一个简单的方法来确定团聚的无定形比的P3 HT和控制的团聚/结晶度的P3 HT在最终的设备通过使用溶剂混合的方法和没有进一步的热处理或预制备的聚合物。P3 HT：PCBM层上的热处理和溶剂浸泡产率的最明显变化是颜色的变化。已经广泛报道，P3 HT的吸收红移，并且在k = 600 nm、550 nm和510 nm处出现一系列电子振动峰。这种红移已被分配到增加的平面化和稳定的P3 HT链，伴随着自堆叠的聚合物。这些自堆积畴的晶体结构已通过使用XRD和TEM解决，并显示了人字形互连的烷基链和1.6 nm的a-维堆积距离。P3 HT链在微晶中的p-p链堆积已被测量为0.38 nm。的人字形结构和平面化的P3 HT与加热已被证实使用heteropathic固态NMR测量。紫外-可见光谱中的红移与P3 HT的团聚程度成比例地发生。P3 HT或P3 HT和PCBM的混合物的纯非晶电子光谱易于测量。也可以在液态下测量溶液的紫外-可见光谱。如果C O M M U N IC A TI O N
In the past several years, polymer–fullerene mixtures have been intensely studied for use in organic solar cells because they can be deposited from solution, are compatible with lowcost roll-to-roll fabrication technology, and have shown high power conversion efficiency (g), up to 4–5%. The best devices consist of a single bulk-heterojunction active layer, in which the polymer (donor) and fullerene (acceptor) are deposited from a common solvent. As the solvent dries the donor and acceptor components separate into domains. The final efficiency of the solar cell has been shown to be extremely sensitive to the size, composition, and crystallinity of the formed domains. Improvement of the morphology in devices fabricated with a mixture of [6,6]-phenyl C61-butyric acid methyl ester (PCBM) and regioregular poly(3-hexylthiophene) (P3HT) has been achieved by using heat-treatment techniques and long-time solvent curing, with resulting record efficiencies. More recently, a method for increasing the crystallinity of the P3HT component has been introduced which involves filtering preformed nanofibers of P3HT out of solution and mixing the prepared nanofiber dispersion with PCBM to increase the efficiency of as-cast devices. Interestingly, the best device performance was achieved by mixing lower-molecular-weight (MW) amorphous P3HT back into the solution to reduce the crystalline content of the active layer and, thereby, to increase connection between crystalline domains. Studies of the MW impact on P3HT/PCBM solar cells have indicated that a large polydispersity and number-average molecular weight (Mn) over 19000 g mol -1 leads to improved efficiency. Morphology studies of organic field-effect transistor (OFET) devices indicate that the increased MW leads to better network formation between crystalline domains. The morphology of these improved devices has been studied using transmission electron microscopy (TEM), grazing-angle X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), NMR, and a variety of other optical and electrical techniques. The morphology studies give a picture of a device in which the P3HT forms aligned/crystalline domains, between which are amorphous segments of P3HT and PCBM. These domains form with larger size and crystallinity for higher heat-treatment temperatures and longer solvent soaking times. Depending on the fabrication and measurement techniques, the aligned domains of P3HT are depicted as fibers or as shapeless masses. The majority of these studies do not, however, allow quantification of the percentage of the P3HT that is agglomerated/ crystalline in the final device. Only by making use of the nanofiber filtration technique have the authors been given the ability to control the crystalline content of the P3HT in solution and in the final device. The disadvantages of this technique are the necessity of more complicated preparation, and filtered P3HT is restricted to a fibrous form that requires the addition of amorphous P3HT to provide connections between crystalline domains. We present here a simple method to determine the agglomerated–amorphous ratio of the P3HT and to control the degree of agglomeration/crystallinity of the P3HT in the final device by using a solvent mixing method and no further heat-treatment or prepreparation of the polymer. The most obvious change that heat-treatment and solvent soaking yield on a P3HT:PCBM layers is the change in color. It has been widely reported that the P3HT absorption red-shifts and a series of vibronic peaks become visible at k ∼ 600 nm, 550 nm, and 510 nm. This red-shift has been assigned to increased planarization and stabilization of the P3HT chains that accompanies self-stacking of the polymer. The crystal structure for these self-stacking domains has been solved by using XRD and TEM, and shows a herringbone interconnection of the alkyl chains and an a-dimension stacking distance of 1.6 nm. The p–p chain stacking of the P3HT chains in crystallites has been measured to be 0.38 nm. The herringbone structure and planarization of the P3HT with heating has been confirmed using heteronuclear solid-state NMR measurements. The red-shift in the UV-vis spectrum occurs proportionally to the degree of agglomeration of the P3HT. The pure amorphous electronic spectrum of P3HT or a mixture of P3HT and PCBM is simple to measure. A solution UV-vis spectrum can also be measured in the liquid state. If C O M M U N IC A TI O N