有机-无机范德瓦尔斯异质结界面的光电过程

Interfacial optoelectronic process in organic-inorganic van der Waals hetero-structure

近年来,有机-无机范德瓦尔斯异质结由于其低成本加工和高性能而在光电应用领域引起了极大的关注.无机的二维材料具有光暗电导比高、载流子迁移率高、稳定性高以及使用寿命长等优点,但是其吸收带窄、可选材料较少、生产成本高;而有机材料具有低成本、透明、柔性、重量轻和易加工等优点,但其介电常数低、载流子迁移率低.如果通过合理的界面设计将二者相结合,扬长避短,有望获得更加优良的光电性能.目前国际上已有多个研究组在这个领域进行了探索性的研究,主要集中在材料的探索和器件功能性的开发,但是其背后的物理原理还不清晰.而微观机理的研究离不开先进的表征技术和测量方法的发展,因此本文旨在总结目前该领域研究进展的基础上,重点介绍有机-无机范德瓦尔斯异质结界面光电子学的表征方法,主要集中在以下3个方面:界面处材料的结构与分子表征、电子结构与局域态表征和微观动力学过程.此外,还针对该领域存在的问题提出了潜在的表征手段,进一步讨论了该领域可能的发展方向.

The tragedy of creating inorganic van der Waals heterostructure has inspired worldwide efforts to integrate various organic materials and distinct inorganic two dimensional(2D) materials to construct organic-inorganic van der walls heterostructures, which hold the great potentials for future flexible electronic and optoelectronic applications. Inorganic 2D materials, e.g., graphene and transition metal dichalcogenides(TMDs), have been extensively investigated for next-generation flexible nanoelectronics, nanophotonics and optoelectronics applications. These materials are benefit in exceptional electronic, optical and optoelectronic properties, such as high tunable optical bandgaps, high carrier mobility, direct-indirect bandgap crossover, and strong spin-orbit coupling etc., but limited in narrow absorption band, high cost and relatively difficult fabrication of high-quality single-crystals. In contrast, organic materials have many advantages, such as low cost, transparency, flexibility, light weight and easy processing, which makes them great candidates for large-area displays, solid-state lighting, sensor and organic solar cell, however, they are shorted in low dielectric constant, low carrier mobility and poor thermo-stability. By marrying the fields of organics and 2D materials, it’s easy to expect outstanding optoelectronic properties that are not present in either material alone. Recently, tremendous efforts have been made to explore the possible combination of organic materials and inorganic 2D materials to create optoelectronic flexible devices of organic-inorganic van der Waals heterostructures with better properties and even new functionalities that are not accessible to us in other heterostructures. Over the past few years, many research groups all over the world have shown substantial progress and excellent results have been generated from such organic-2D material heterostructures. Among them, finding the possible combination of organics and 2D materials, investigating the properties of such heterostructures, and testing the functionality of the corresponding devices are the main targets currently in this field. The optimization of such devices with excellent performance is strongly relied on a fundamental understanding of the organic-2D material interface. For instance, the band alignment at the interface of organic and 2D TMD directly determine the basic physical properties of heterostructures. However, the interfacial features of such heterostructures, e.g., interfacial charge transfer, surface screening effect, molecular doping and so on, are barely known. It’s therefore vital to study the underlying physical mechanism. Here, we review the latest progress of this field first:(1) The fabrication of the organic-2D material heterostructures and the devices;(2) the performances of such devices. Substantially, the characterization methods and the related techniques are fully reviewed and discussed based on the specific demands of organic-2D material heterostructures. Three parts were included:(1) The characterization of interfacial material structure and molecular conformation;(2) interfacial electronic structure and defects;(3) carrier dynamics. The progress in this field including the utilization of several key techniques including transmission electron microscopy, scanning probe microscopy and transient absorption spectroscopy et al., are comprehensively reviewed, and the potential characterization and measurement methods are discussed in detail. Besides, the main challenges of such heterostructures in future flexible electronic and optoelectronic applications are discussed as well. We believe this review will therefore shed light on the booming the development of this field by guiding the selection of the proper materials, the creation of the desired organic-2D material heterostructures and the optimization of the devices.