ABSTRACT

Hybrid interfaces formed by inorganic semiconductors and organic molecules are intriguing materials for opto-electronics. Interfacial charge transfer is primarily responsible for their peculiar electronic structure and optical response. Hence, it is essential to gain insight into this fundamental process also beyond the static picture. Ab initio methods based on real-time time-dependent density-functional theory coupled to the Ehrenfest molecular dynamics scheme are ideally suited for this problem. We investigate a laser-excited hybrid inorganic/organic interface formed by the electron acceptor molecule 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane (F4TCNQ) physisorbed on a hydrogenated silicon cluster, and we discuss the fundamental mechanisms of charge transfer in the ultrashort time window following the impulsive excitation. The considered interface is p-doped and exhibits charge transfer in the ground state. When it is excited by a resonant laser pulse, the charge transfer across the interface is additionally increased, but contrary to previous observations in all-organic donor/acceptor complexes, it is not further promoted by vibronic coupling. In the considered time window of 100 fs, the molecular vibrations are coupled to the electron dynamics and enhance intramolecular charge transfer. Our results highlight the complexity of the physics involved and demonstrate the ability of the adopted formalism to achieve a comprehensive understanding of ultrafast charge transfer in hybrid materials.

摘要

由无机半导体和有机分子形成的混合界面是光电子的诱人材料。界面电荷转移主要负责其特殊的电子结构和光学响应。因此，除了静态画面以外，还必须深入了解此基本过程。从头算基于实时时变密度函数理论并结合Ehrenfest分子动力学方案的方法非常适合此问题。我们研究了由电子受体分子2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane（F4TCNQ）物理吸附在氢化硅簇上形成的激光激发无机/有机杂化界面，并且讨论了脉冲激励后超短时间窗口中电荷转移的基本机制。考虑的接口是p掺杂并在基态下表现出电荷转移。当它被共振激光脉冲激发时，通过界面的电荷转移会进一步增加，但是与以前在全有机供体/受体复合物中观察到的相反，它不会通过振动耦合进一步促进。在所考虑的100 fs的时间窗口中，分子振动与电子动力学耦合，并增强了分子内电荷转移。我们的结果突出了所涉及的物理学的复杂性，并证明了所采用的形式主义能够全面了解混合材料中的超快电荷转移。