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Stable Solar Cells through Controlled Block Copolymer Self- Assembly and Cooperative Hydrogen Bonding Interactions.

机译：通过控制嵌段共聚物的自组装和协同氢键相互作用实现稳定的太阳能电池。

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摘要

Current state-of-the-art polymer solar cells adopt the bulk-heterojunction (BHJ) morphologies where the electron donors (i.e. conjugated polymer) and electron acceptors (i.e. fullerenes) as active layers are mixed in an intimate way. The phase separation that modulates the exciton diffusion and charge transport in the current BHJ morphology is an uncontrolled process and thus results in random domain sizes of the polymer/fullerene blend. In addition, the polymer and fullerenes in the blend are intrinsically two immiscible materials and they tend to undergo macrophase separation eventually, which leads to deteriorated device performance. One way to address the abovementioned issues is to attach fullerenes onto the polymers covalently or non-covalently, aiming at controlling the phase separations and suppressing the macrophase separation between the polymer and fullerenes. However, either the device performance or the morphology of the active layer is not satisfactory to meet our needs.;In my dissertation, I combine block copolymer self-assembly and hydrogen bonding interactions to construct morphologies that are not only thermally stable, but also controllable on the nanoscale. The controllability of the blend morphologies is simply achieved by tuning the fullerene contents in the polymer/fullerene blend. Moreover, solar cells fabricated from such polymer/fullerene blends perform in a comparable way with the benchmark BHJ solar cell however with much enhanced device thermal stabilities. I believe this methodology will shed light on the polymer design and morphology control for the chemists and engineers in this field to obtain high-performing solar cells with better thermal stabilities.;Specifically, I started this project by synthesizing the poly(3-hexylthiophene) (P3HT) based all-conjugated block copolymer (BCP) (P4) selectively functionalized with diaminopyrimidine moieties and a thymine tethered fullerene derivative (F1). Strong interactions between P4 and F1 through the "three-point" complementary hydrogen bonding are studied by 1H NMR spectroscopy, fluorescent spectroscopy, differential scanning calorimetry (DSC) and atomic force microscopy (AFM). Solar cells employing P4 and F1 at different weight ratios as active layers are fabricated and tested. Although the photovoltaic performances of P4/F1 solar cells were not good, the morphology of the blend exhibited tunable nature simply by adjusting the F1 ratios in the blend.;Secondly, I modified the synthesis of the BCP and obtained a polythiophene diblock copolymer selectively functionalized with 1-N-hexyl isoorotic acid (IOA) moieties (P8) with a longer P3HT block and a 2, 6-diaminopyridine tethered fullerene derivative (F2). Solar cells employing P8 blended with different weight ratios of F2 and phenyl-C61-butyric acid methyl ester (PCBM) were fabricated and tested. The best power conversion efficiencies (PCEs) were observed in devices made from P8/F2 blends (10/8 by wt.) and ternary blends of P8/F2/PCBM (10/4/4 by wt.) as active layers, which is much better than those from P4/F2 blends. Thermal stabilities of these solar cells were studied in detail by aging tests and corresponding morphological changes were closely monitored by absorption spectroscopy, optical microscopy, AFM and X-ray analyses. The "three-point" complementary hydrogen bonding interactions between P8 and F2, in cooperation with block polymer self-assembly, were found to not only improve the thermal stability of solar cells significantly but also lead to tunable active layer morphologies. Nanostructures with long-range order were identified in blend films employing P8, which has never been observed before in conventional polymer/fullerene bulk heterojunction (BHJ) films.;Thirdly, by employing the P8/PCBM blend, I further developed a novel methodology of constructing stable and controllable conjugated polymer (CP)/fullerene nanostructures. By building in non-covalent interactions between CP nanofibers (NFs) and fullerene derivatives, supramolecular polymer/fullerene composite NFs are obtained in solution for the first time. Specifically, self-assembly of P8 in mixed solvents leads to well-defined NFs decorated with IOA groups on the periphery, onto which PCBM molecules are subsequently attached non-covalently. Formation of such complex structures are studied in detail and confirmed by UV-Vis absorption spectroscopy, transmission electron microscopy (TEM), atomic force microscopy (AFM), and X-ray scattering measurements. Application of these composite NFs (P8/PCBM 10/4, wt/wt) in organic photovoltaic (OPV) devices not only leads to superior performance but also much improved thermal stability and rarely observed long-range ordered morphology, when compared with conventional bulk heterojunction (BHJ) devices.;Last but not least, I also investigated the P8/F2 composite nanofibers formation and found out that the width of the composite nanofibers not only depends on the type of the fullerenes added, but also the amount of fullerenes mixed in the blends. Besides, solar cells fabricated from the composite nanofibers blends outperformed their conventional BHJ devices under the same fabricating conditions. Through 1H NMR observations, I also proposed a formation mechanism of the P8 nanofibers that agrees well with our experimental results.
机译：当前的最先进的聚合物太阳能电池采用体-异质结（BHJ）形态，其中作为活性层的电子给体（即共轭聚合物）和电子受体（即富勒烯）以紧密的方式混合。在当前的BHJ形态中调节激子扩散和电荷传输的相分离是不受控制的过程，因此导致聚合物/富勒烯共混物的畴尺寸无规。另外，共混物中的聚合物和富勒烯本质上是两种不混溶的材料，它们最终趋于经历宏观相分离，这导致器件性能下降。解决上述问题的一种方法是将富勒烯共价或非共价连接到聚合物上，旨在控制相分离并抑制聚合物和富勒烯之间的大相分离。然而，无论是器件性能还是活性层的形貌都不能令人满意地满足我们的需求。在我的论文中，我结合了嵌段共聚物的自组装和氢键相互作用来构建不仅热稳定而且可控的形貌。在纳米级。通过调节聚合物/富勒烯共混物中的富勒烯含量，可以简单地实现共混物形态的可控制性。此外，由这种聚合物/富勒烯共混物制成的太阳能电池以与基准BHJ太阳能电池相当的方式运行，但是具有更高的器件热稳定性。我相信这种方法学将为该领域的化学家和工程师提供聚合物设计和形态控制方面的帮助，从而获得具有更好热稳定性的高性能太阳能电池。具体来说，我通过合成聚（3-己基噻吩）开始了这个项目（P3HT）基全共轭嵌段共聚物（BCP）（P4）用二氨基嘧啶部分和胸腺嘧啶系留的富勒烯衍生物（F1）选择性官能化。通过1H NMR光谱，荧光光谱，差示扫描量热法（DSC）和原子力显微镜（AFM）研究了P4和F1之间通过“三点”互补氢键之间的强相互作用。制作并测试了采用不同重量比的P4和F1作为有源层的太阳能电池。尽管P4 / F1太阳能电池的光伏性能不佳，但仅通过调节混合物中的F1比例，混合物的形态就表现出可调性。具有更长的P3HT嵌段的1-N-己基异戊酸（IOA）部分（P8）和2，6-二氨基吡啶系留的富勒烯衍生物（F2）。制备并测试了采用掺有不同重量比的F2和苯基-C61-丁酸甲酯（PCBM）的P8的太阳能电池。在由P8 / F2共混物（10/8 wt。）和P8 / F2 / PCBM三元共混物（10/4/4 wt。）作为活性层制成的设备中，观察到最佳的功率转换效率（PCE）。比P4 / F2混合物的要好得多。通过老化测试详细研究了这些太阳能电池的热稳定性，并通过吸收光谱，光学显微镜，AFM和X射线分析密切监测了相应的形态变化。发现P8和F2之间的“三点”互补氢键相互作用与嵌段聚合物的自组装协同作用，不仅显着提高了太阳能电池的热稳定性，而且导致了可调节的活性层形貌。在使用P8的共混膜中鉴定出具有长程有序的纳米结构，这在传统的聚合物/富勒烯本体异质结（BHJ）膜中从未见过。第三，通过使用P8 / PCBM共混，我进一步开发了一种新的方法构建稳定且可控的共轭聚合物（CP）/富勒烯纳米结构。通过建立CP纳米纤维（NFs）与富勒烯衍生物之间的非共价相互作用，首次在溶液中获得了超分子聚合物/富勒烯复合材料NFs。具体而言，P8在混合溶剂中的自组装会导致轮廓分明的NF，这些NF周围装饰有IOA基团，随后PCBM分子非共价连接到其上。对这种复杂结构的形成进行了详细研究，并通过UV-Vis吸收光谱，透射电子显微镜（TEM），原子力显微镜（AFM）和X射线散射测量得到了证实。与常规本体相比，这些复合NF（P8 / PCBM 10/4，wt / wt）在有机光伏（OPV）器件中的应用不仅可带来出色的性能，而且还大大提高了热稳定性，并且很少观察到远距离有序形态异质结（BHJ）器件。；最后但并非最不重要的，我还研究了P8 / F2复合纳米纤维的形成，发现复合纳米纤维的宽度不仅取决于所添加富勒烯的类型，还取决于掺混物中富勒烯的混合量。此外，在相同的制造条件下，由复合纳米纤维混合物制成的太阳能电池的性能优于传统的BHJ器件。通过1 H NMR观察，我还提出了P8纳米纤维的形成机理，该机理与我们的实验结果非常吻合。

著录项

  • 作者

    Li, Fei.;

  • 作者单位

    The University of New Mexico.;

  • 授予单位 The University of New Mexico.;
  • 学科 Chemistry Physical.;Chemistry Organic.;Chemistry Polymer.;Engineering Materials Science.;Nanotechnology.;Alternative Energy.
  • 学位 Ph.D.
  • 年度 2014
  • 页码 258 p.
  • 总页数 258
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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