Molecular Order in High-Efficiency Polymer/Fullerene Bulk Heterojunction Solar Cells
Molecular Order in High-Efficiency Polymer/Fullerene Bulk Heterojunction Solar Cells
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DOI：
10.1021/nn202951e
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发表时间：
2011-10-01
期刊：
影响因子：
17.1
通讯作者：
DeLongchamp, Dean M.
中科院分区：
文献类型：
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作者：
Hammond, Matthew R.;Kline, R. Joseph;DeLongchamp, Dean M.
我们报告了基于噻吩并[3,4-b]噻吩-替代苯并二噻吩共聚物（PTB7）的本体异质结（BHJ）有机光伏电池活性层的有序性、分子取向和纳米级形态的定量测量，该共聚物已被证明与[6,6]-苯基-C71-丁酸甲酯（PC71BM）混合时可产生非常高的功率转换效率。在聚合物中发现了令人惊讶的低有序度——本体异质结中的有序度远低于纯 PTB7 中的有序度。 X 射线衍射数据在有序区域内产生了聚合物 pi 堆积方向的几乎完整的取向分布，揭示了对垂直方向（“正面”）的 pi 堆积的适度偏好。通过将偏振吸收光谱的分子取向信息与衍射得到的有序材料的取向分布相结合，我们提出了一个描述 PTB7 分子取向分布（有序和无序）的模型，其中有序聚合物的分数作为模型参数。该模型显示 PTB7/PC71BM 共混物中仅一小部分（约 20%）聚合物是有序的。能量过滤透射电子显微镜显示PTB7/PC71BM的形态由富含聚合物区域分隔的纳米级富勒烯聚集体组成。相对于不含 DIO 的共混薄膜，将二碘辛烷 (DIO) 作为加工添加剂添加到浇铸溶剂中会产生更小的域和更精细的互穿 BHJ 形态。
We report quantitative measurements of ordering, molecular orientation, and nanoscale morphology in the active layer of bulk heterojunction (BHJ) organic photovoltaic cells based on a thieno[3,4-b]thiophene-alt-benzodithiophene copolymer (PTB7), which has been shown to yield very high power conversion efficiency when blended with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM). A surprisingly low degree of order was found in the polymer-far lower in the bulk heterojunction than in pure PTB7. X-ray diffraction data yielded a nearly full orientation distribution for the polymer pi-stacking direction within well-ordered regions, revealing a moderate preference for pi-stacking in the vertical direction ("face-on"). By combining molecular orientation Information from polarizing absorption spectroscopies with the orientation distribution of ordered material from diffraction, we propose a model describing the PTB7 molecular orientation distribution (ordered and disordered), with the fraction of ordered polymer as a model parameter. This model shows that only a small fraction (approximate to 20%) of the polymer in the PTB7/PC71BM blend is ordered. Energy-filtered transmission electron microscopy shows that the morphology of PTB7/PC71BM is composed of nanoscale fullerene-rich aggregates separated by polymer-rich regions. The addition of dliodooctane (DIO) to the casting solvent, as a processing additive, results in smaller domains and a more finely interpenetrating BHJ morphology, relative to blend films cast without DIO.