Solution-processed 2D van der Waals networks: Fabrication strategies, properties, and scalable device applications

Solution-based processing of two-dimensional (2D) materials has garnered significant interest as a facile and versatile route for the large-scalable production of 2D material films. Despite the benefits in process, these films were not considered suitable for device applications during the early stages of research because their electronic properties were far from those of 2D materials obtained through micromechanical exfoliation or chemical vapor deposition. Due to the small lateral dimensions and polydisperse thickness of constituent 2D nanosheets, the resulting film tends to be porous and exhibits numerous inter-sheet junctions, primarily contacting edge-to-edge. This nanosheet morphology leads to poor electrical conductivity of the network, and also hinders the film functioning as a semiconductor or an insulator. To produce ultrathin 2D nanosheets with narrow thickness distribution and large lateral sizes, various chemical exfoliation strategies have been explored, but these are limited by long process times, involvement of harsh chemicals, and/or undesired structural damage or phase changes. Recent breakthroughs in electrochemical exfoliation using tetraalkylammonium intercalants enabled the production of high-quality 2D nanosheets with structural characteristics favorable for producing ultrathin, conformal films of 2D materials, which allow for scalable production of high-performance electronic components that can readily be assembled into functional devices via solution-processing. In this review article, we aim to offer an extensive introduction solution-based processing techniques for acquiring 2D nanosheets, their subsequent assembly into thin films, and their diverse applications, primarily focusing on electronics and optoelectronics but also extending to other fields. Remaining challenges and potential avenues for advancement will also be discussed.