Injection from metallic electrodes serves as a main channel of charge generation in organic semiconducting devices and the quantum effect is normally regarded as essential. We develop a dynamic approach based upon the surface-hopping (SH) algorithm and classical device modeling, by which both quantum tunneling and thermionic emission of charge-carrier injection at metal-organic interfaces are concurrently investigated. The injected charges from a metallic electrode are observed to spread quickly onto the organic molecules, followed by an accumulation close to the interface, induced by the built-in electric field. We compare the Ehrenfest dynamics on the mean-field level and the SH algorithm by simulating the temperature dependence of the charge-injection dynamics and it is found that the former leads to an improper result, that the injection efficiency decreases with increasing temperature in the room-temperature regime while the SH results are credible. The relationship between the injected charges and the applied bias voltage suggests that it is the quantum tunneling that dominates the low-threshold injection characteristics in molecular crystals, which is further supported by the calculation results of a small entropy change during the injection process. An optimum interfacial width for the charge-injection efficiency at the interface is also quantified and can be utilized to understand the role of the interfacial buffer layer in practical devices.

中文翻译：

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模拟金属-有机界面处的量子隧穿和热电子发射的统一动态方法

在有机半导体器件中，金属电极的注入是电荷产生的主要通道，通常认为量子效应是必不可少的。我们开发了一种基于表面跳变（SH）算法和经典器件建模的动态方法，通过该方法，同时研究了金属有机界面处的量子隧穿和电荷载流子注入的热电子发射。观察到从金属电极注入的电荷迅速扩散到有机分子上，随后由于内置电场而在界面附近积累。通过模拟电荷注入动力学的温度依赖性，我们比较了Ehrenfest动力学和均值场水平上的算法，发现前者会导致不正确的结果，在室温下，注射效率随温度的升高而降低，而SH的结果是可信的。注入的电荷与施加的偏置电压之间的关系表明，量子隧穿控制着分子晶体的低阈值注入特性，这在注入过程中熵的小变化计算结果中得到了进一步证明。界面上电荷注入效率的最佳界面宽度也被量化，可以用来理解界面缓冲层在实际设备中的作用。注入的电荷与施加的偏置电压之间的关系表明，量子隧穿控制着分子晶体的低阈值注入特性，这在注入过程中熵的小变化计算结果中得到了进一步证明。界面上电荷注入效率的最佳界面宽度也被量化，可以用来理解界面缓冲层在实际设备中的作用。注入的电荷与施加的偏置电压之间的关系表明，量子隧穿控制着分子晶体的低阈值注入特性，这在注入过程中熵的小变化计算结果中得到了进一步证明。界面上电荷注入效率的最佳界面宽度也被量化，可以用来理解界面缓冲层在实际设备中的作用。