有机半导体中缺陷态对界面能级调控及载流子传输性能影响的研究

Density of gap states (DOGS) in organic semiconductors strongly affect charge transport properties in related organic devices. The energy level distributions of gap states and their concentrations have strong impacts on the energy level alignment both at organic-inorganic interfaces and organic-organic interfaces. DOGS in the bulk of organic films also can limit the charge mobility and films conductivity. Thus, a deeper understanding of the gap states in energy level distributions and concentrations is necessary. In particular, the effective methods to reduce those density of gap states should be further studied. In this project, we are going to use the low photon energy photoelectron spectroscopy and admittance spectroscopy to investigate: (1) how the density of gap states in films surface affect the energy level alignment in organic-inorganic and organic-organic interface, (2) how the charge transport properties can be influenced by those gap states in the bulk of organic films, and (3) the effective ultralow organic doping methods to reduce the density of gap states. After carefully study through electronic structures and devices characteristics, a systematic model based on density of gap states will be proposed to explain changes of gap states from the interface to the bulk. Finally, a high conductivity films with low density of gap states will be realized. Our research project will give a better understanding of operational mechanism of organic devices and a new optimization to the device structure, which will hopefully inspire the future work.

有机半导体薄膜中，各种缺陷态直接影响着器件中载流子的传输性能。界面缺陷态分布及其浓度直接影响着有机-无机界面、有机-有机界面的能级排布；体内缺陷态浓度影响着载流子的迁移率、薄膜的电导率。因而，进一步理解缺陷态及其浓度分布对有机半导体薄膜能级排布的影响，并有效调控这些缺陷态十分有意义。本项目通过低能量光源光电子能谱仪与阻抗仪来系统研究有机半导体薄膜中表面缺陷态浓度与界面能级排布关系；体内缺陷态浓度大小如何影响载流子输运效率；以及超低浓度掺杂如何有效减小（“钝化”）体缺陷态等。通过这些研究，我们将建立有机半导体薄膜中不同缺陷态、浓度分布模型，并制备出低缺陷态浓度的有机薄膜。通过本项目的研究，能进一步完善有机半导体材料性能、明析其器件的工作机理，并为设计更好的光电器件结构提供实验、理论基础。

有机半导体薄膜中，各种缺陷态直接影响着器件中载流子的传输性能。界面缺陷态分布及其浓度直接影响着有机-无机界面、有机-有机界面的能级排布；体内缺陷态浓度影响着载流子的迁移率、薄膜的电导率。因而，进一步理解缺陷态及其浓度分布对有机半导体薄膜能级排布的影响，并有效调控这些缺陷态十分有意义。通过本项目的研究，我们揭示了有机半导体材料中界面能级排布的定量机理：最小注入势垒与有机层的高斯分布有直接关系，界面缺陷态会引起界面注入势垒的增加。结合紫外光电子能谱仪与理论计算，我们发现有机热蒸发的薄膜中存在的缺陷态直接影响着费米能级在能隙中的位置，通过超低浓度的有机掺杂，可以有效“钝化”这些缺陷态，调节有机掺杂的效果。同样我们也结合制备相关器件，通过阻抗谱来研究了这些缺陷态对叠层OLED器件内部连接层载流子的产生机理，发现MoO3中的缺陷态有利于在较低的开启电压下产生电子和空穴，实现叠层器件的正常工作。通过使用角分辨的光电子能谱仪，我们同样也研究了有机（有机-无机）单晶中的能带与晶格振动（声子）的关系，揭示了有机分子的热运动会直接影响能带的色散关系，引起能带的分裂，从而会改变空穴的有效质量；结合有机-无机钙钛矿单晶发现其能带色散关系满足立方相的能带结构，首次通过实验给出了其空穴有效质量，揭示了其代表的杂化太阳能器件优异性能的物理机制。

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