Felekidis N, Melianas A, Kemerink M
Complex Materials and Devices, Department of Physics, Chemistry and Biology, Linköping University, 58183 Linköping, Sweden.
Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, United States.
J Phys Chem Lett. 2020 May 7;11(9):3563-3570. doi: 10.1021/acs.jpclett.0c00945. Epub 2020 Apr 22.
The photon energy dependence of long-range charge separation is studied for two prototypical polymer:fullerene systems. The internal quantum efficiency (IQE) of PCDTBT:PCBM is experimentally shown to be independent of the excitation energy. In contrast, for TQ1:PCBM the IQE is strongly energy-dependent for excitation energies close to charge transfer (CT) electroluminescence peak maximum while it becomes energy-independent at higher excitation energies. Kinetic Monte Carlo simulations reproduce the experimental IQE and reveal that the photon energy-dependence of the IQE is governed by charge delocalization. Efficient long-range separation at excitation energies corresponding to the CT electroluminescence peak maximum or lower requires an initial separation of the hole-electron pair by ∼4-5 nm, whereas delocalization is less important for charge separation at higher photon energies. Our modeling results suggest that a phenomenological reciprocity between CT electroluminescence and external quantum efficiency does not necessarily prove that commonly employed reciprocity relations between these spectra are valid from a fundamental perspective.
富勒烯体系，研究了远程电荷分离的光子能量依赖性。实验表明，聚[2,6-(4,4-双十二烷基-4H-环戊二烯并[2,1-b:3,4-b']二噻吩)-alt-4,7-二噻吩并[2,1,3]噻二唑]:[6,6]-苯基-C61-丁酸甲酯（PCDTBT:PCBM）的内量子效率（IQE）与激发能量无关。相比之下，对于四喹啉并苝二亚胺（TQ1）:PCBM，在接近电荷转移（CT）电致发光峰值最大值的激发能量下，IQE强烈依赖于能量，而在较高激发能量下则与能量无关。动力学蒙特卡罗模拟重现了实验IQE，并揭示IQE的光子能量依赖性受电荷离域控制。在对应于CT电致发光峰值最大值或更低的激发能量下实现有效的远程分离，需要空穴-电子对初始分离约4-5纳米，而对于较高光子能量下的电荷分离，离域的重要性较低。我们的建模结果表明，CT电致发光与外量子效率之间的唯象互易性并不一定证明从基本层面来看这些光谱之间常用的互易关系是有效的。
