Comparison of the Photovoltaic Characteristics and Nanostructure of Fullerenes Blended with Conjugated Polymers with Siloxane-Terminated and Branched Aliphatic Side Chains
Comparison of the Photovoltaic Characteristics and Nanostructure of Fullerenes Blended with Conjugated Polymers with Siloxane-Terminated and Branched Aliphatic Side Chains
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DOI：
10.1021/cm303572d
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发表时间：
2013-02-12
影响因子：
8.6
通讯作者：
Bao, Zhenan
中科院分区：
文献类型：
--
作者：
Kim, Do Hwan;Ayzner, Alexander L.;Bao, Zhenan
基于共轭聚合物与富勒烯混合物的全有机本体异质结太阳能电池最近已经突破了 8% 的效率大关，并且正在向工业相关的类似于 45% 的阈值迈进。使用低带隙共轭聚合物，我们最近表明聚合物侧链工程可以显着提高面内载流子迁移率。在本文中，我们研究了硅氧基侧链衍生化在控制聚合物：[6,6]-苯基-C[71]-丁酸甲酯（PC71BM）共混物的光伏性能方面的有效性，及其对有机太阳能电池相关面外方向电荷传输的影响。我们发现，在纯共混物中，具有甲硅烷氧基侧链的聚合物（PII2T-Si）的光电流是使用具有支化脂肪族侧链的聚合物（PII2T-ref）的共混物中的光电流的4倍。这种差异是由于 PII2T-Si 具有较大的面外空穴迁移率，这是由大部分面朝上的微晶取向以及更优化的纳米级聚合物：PC71BM 混合带来的。然而，在将常见的加工添加剂 1,8-二碘辛烷 (DIO) 加入到旋涂共混溶液中并进行优化后，PII2T-ref:PC71BM OPV 器件的性能得到了很大的改善，成为性能更好的器件，几乎与 DIO 浓度 (>1%) 无关。我们发现，DIO 的精确含量在决定 PII2T-Si:PC71BM 的效率方面发挥着更大的作用，即使在最大效率下，器件性能也落后于优化的 PII2T-ref:PC71BM 混合物。结合使用原子力显微镜和小角和广角 X 射线散射，我们能够阐明与 DIO 引起的纳米级形态和共混膜中分子堆积变化相关的形态修饰。
All-organic bulk heterojunction solar cells based on blends of conjugated polymers with fullerenes have recently surpassed the 8% efficiency mark and are well on their way to the industrially relevant similar to 45% threshold. Using a low band-gap conjugated polymer, we have recently shown that polymer side chain engineering can lead to dramatic improvement in the in-plane charge carrier mobility. In this article, we investigate the effectiveness of siloxy side chain derivatization in controlling the photovoltaic performance of polymer: [6,6]-phenyl-C[71]-butyric acid methyl ester (PC71BM) blends and hence its influence on charge transport in the out-of-plane direction relevant for organic solar cells. We find that, in neat blends, the photocurrent of the polymer with siloxy side chains (PII2T-Si) is 4 times greater than that in blends using the polymer with branched aliphatic side chains (PII2T-ref). This difference is due to a larger out-of-plane hole mobility for PII2T-Si brought about by a largely face-on crystallite orientation as well as more optimal nanoscale polymer:PC71BM mixing. However, upon incorporating a common processing additive, 1,8-diiodooctane (DIO), into the spin-casting blend solution and following optimization, the PII2T-ref:PC71BM OPV device performance undergoes a large improvement and becomes the better-performing device, almost independent of DIO concentration (>1%). We find that the precise amount of DIO plays a larger role in determining the efficiency of PII2T-Si:PC71BM, and even at its maximum, the device performance lags behind optimized PII2T-ref:PC71BM blends. Using a combination of atomic force microscopy and small- and wide-angle X-ray scattering, we are able to elucidate the morphological modifications associated with the DIO-induced changes in both the nanoscale morphology and the molecular packing in blend films.