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Polarization anisotropy of charge transfer absorption and emission of aligned polymer: fullerene blend films

机译：取向聚合物的电荷转移吸收和发射的极化各向异性：富勒烯共混膜

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摘要

An improved understanding of the electronic structure of interfacial charge transfer (CT) states is of importance due to their crucial role in charge carrier generation and recombination in organic donor-acceptor (DA) solar cells. DA combinations with a small difference between the energy of the CT state (E_(cr)) and energy of the donor exciton (E_(d*)) are of special interest since energy losses due to electron transfer are minimized, resulting in an optimized open-circuit voltage. In that case, the CT state can be considered as a resonance mixture, containing character of a fully ionic state (D~+A~-) and of the local polymer excited state (D*A). We show that the D*A contribution to the overall CT state wave function can be determined by measurements of the polarization anisotropy of CT absorption and emission of polymenfullerene blends with aligned polymer chains. We study two donor polymers, P3HT and TQ1, blended with fullerene acceptors with different ionization potentials, allowing variation of the E(d*) — E_(CT) difference. We find that, upon decreasing E_(d*) — E_(ct) the local excitonic D* A character of the CT state increases, resulting in a decreased fraction of charge transferred and an increased transition dipole moment. For typical polymer:fullerene systems, this effect is expected to become detrimental for device performance if E_(d*) — E_(CT) < 0.1 eV. This however, depends on the electronic coupling between D* A and D~+A~-, which we experimentally estimate to be ~ 6 meV for the TQ1 :PCBM system.
机译：由于界面电荷转移在有机供体-受体（DA）太阳能电池中电荷载流子的产生和复合中起着至关重要的作用，因此对界面电荷转移（CT）态电子结构的更好理解至关重要。由于CT态的能量（E_（cr））和施主激子的能量（E_（d *））之间的差异很小，因此DA组合特别受关注，因为可以将由于电子转移引起的能量损失降到最低，从而实现优化开路电压。在那种情况下，CT状态可以被认为是一种共振混合物，它具有完全离子态（D〜+ A〜-）和局部聚合物激发态（D * A）的特性。我们表明，D * A对整个CT状态波函数的贡献可以通过测量CT吸收和发射的聚偏富勒烯共混物与排列的聚合物链的偏振各向异性来确定。我们研究了两种供体聚合物P3HT和TQ1，它们与具有不同电离势的富勒烯受体混合，从而允许E（d *）-E_（CT）差异的变化。我们发现，随着E_（d *）-E_（ct）的减小，CT态的局部激子D * A的特性增加，从而导致电荷转移分数的降低和跃迁偶极矩的增加。对于典型的聚合物：富勒烯体系，如果E_（d *）-E_（CT）<0.1 eV，则预期该效应会对器件性能产生不利影响。但是，这取决于D * A和D〜+ A〜-之间的电子耦合，我们对TQ1：PCBM系统的实验估计约为〜6 meV。

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  • 来源
    《Physical review》 |2012年第3期|p.035212.1-035212.9|共9页
  • 作者

    Koen Vandewal; Kristofer Tvingstedt; Olle Inganas;

  • 作者单位

    Biomolecular and Organic Electronics, IFM, Linkoping University, SE-581 83 Linkoping, Sweden,Department of Materials Science and Engineering,Geballe Laboratory for Advanced Materials, McCullough Building,Stanford University, Stanford, California 94305, United States;

    Biomolecular and Organic Electronics, IFM, Linkoping University, SE-581 83 Linkoping, Sweden;

    Biomolecular and Organic Electronics, IFM, Linkoping University, SE-581 83 Linkoping, Sweden;

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  • 正文语种 eng
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  • 关键词

    photoconduction and photovoltaic effects; polymers; organic compounds;

    机译：光电导和光电效应;聚合物有机化合物;

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