Causa' Martina, Ramirez Ivan, Martinez Hardigree Josue F, Riede Moritz, Banerji Natalie
Department of Chemistry and Biochemistry , University of Bern , Freiestrasse 3 , 3012 Bern , Switzerland.
Clarendon Laboratory, Department of Physics , University of Oxford , Parks Road , OX1 3PU , Oxford , United Kingdom.
J Phys Chem Lett. 2018 Apr 19;9(8):1885-1892. doi: 10.1021/acs.jpclett.8b00520. Epub 2018 Mar 30.
The well known organic semiconductor C is attracting renewed attention due to its centimeter-long electron diffusion length and high performance of solar cells containing 95% fullerene, yet its photophysical properties remain poorly understood. We elucidate the dynamics of Frenkel and intermolecular (inter-C) charge-transfer (CT) excitons in neat and diluted C films from high-quality femtosecond transient absorption (TA) measurements performed at low fluences and free from oxygen or pump-induced photodimerization. We find from preferential excitation of either species that the CT excitons give rise to a strong electro-absorption (EA) signal but are extremely short-lived. The Frenkel exciton relaxation and triplet yield strongly depend on the C aggregation. Finally, TA measurements on full devices with applied electric field allow us to optically monitor the dissociation of CT excitons into free charges for the first time and to demonstrate the influence of cluster size on the spectral signature of the C anion.
著名的有机半导体C因其厘米级的电子扩散长度以及含95%富勒烯的太阳能电池的高性能而再次受到关注，但其光物理性质仍未得到很好的理解。我们通过在低通量下进行的、无氧气或泵浦诱导光二聚化的高质量飞秒瞬态吸收（TA）测量，阐明了纯净和稀释的C薄膜中Frenkel激子和分子间（C间）电荷转移（CT）激子的动力学。我们从对任一物种的优先激发中发现，CT激子会产生强烈的电吸收（EA）信号，但寿命极短。Frenkel激子的弛豫和三重态产率强烈依赖于C的聚集。最后，对施加电场的完整器件进行TA测量，使我们首次能够光学监测CT激子解离为自由电荷的过程，并证明团簇尺寸对C阴离子光谱特征的影响。
