声子辅助的PCBM聚集体中的超快电荷分离
Phonon-Assisted Ultrafast Charge Separation in a Realistic PCBM Aggregate
摘要：
有机太阳能电池必须将强束缚的电子-空穴对分离成自由电荷。这是在电子供体和受体有机半导体之间的界面处实现的。最常用的电子受体是富勒烯衍生物PCBM。电子-空穴分离已经在飞秒时间尺度上被观察到，这与传统的Marcus有机输运理论是不相容的。在这项工作中，我们表明，超快的电荷传输PCBM产生的电子本征态的范围广泛，提供了三个紧密间隔的离域带附近的LUMO水平的存在。振动波动使这些频带之间的快速跃迁，这驱动$\sim$ 3 nm的电子输运在100 fs内。所有这一切都表明在一个现实的紧束缚哈密顿包含不大于8毫电子伏的转移积分。
英文摘要：
Organic solar cells must separate strongly bound electron-hole pairs into free charges. This is achieved at interfaces between electron donor and acceptor organic semiconductors. The most popular electron acceptor is the fullerene derivative PCBM. Electron-hole separation has been observed on femtosecond timescales, which is incompatible with conventional Marcus theories of organic transport. In this work we show that ultrafast charge transport in PCBM arises from its broad range of electronic eigenstates, provided by the presence of three closely spaced delocalised bands near the LUMO level. Vibrational fluctuations enable rapid transitions between these bands, which drives an electron transport of $\sim$3 nm within 100 fs. All this is demonstrated within a realistic tight binding Hamiltonian containing transfer integrals no larger than 8 meV.
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