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

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, its 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. Its 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.