2D materials go beyond graphene for electronics
The demand for miniaturisation of electronics is continuing to grow, but the industry is now nearing the scaling limit for silicon materials. Lately, 2D materials have emerged as promising candidates for use in miniaturised electronic and optoelectronic devices due to their distinct properties, alongside atomically-thin dimensions. With graphene being the first 2D material studied in detail, there is now a focus on other materials with vastly different properties for new applications. Within the EU-funded project DEMONH, scientists have studied the electronic and optical properties of a 2D semiconducting material known as molybdenum disulphide (MoS2) and of promising hybrid materials known as lead halide perovskites. Perfection is not everything Point defects such as vacancies and impurities are essential in electronics. “Although point defects can be sometimes deemed as a considerable drawback for realising certain electronic operations, each single type of defect can cause a profound change to the material properties. In particular, the ubiquitous presence of defects can dramatically enhance the physical, electrochemical and optoelectronic response of 2D materials,” points out project coordinator David Beljonne. Scientists have been primarily concerned with the influence of point defects that are either created intentionally to increase density of anchoring sites or are created naturally during material synthesis. In the former case, anchoring nanoparticles on defect sites of MoS2 under light illumination can add to the complexity of the material’s functional behaviour. Another focus was on establishing a general theoretical framework that can capture both the photophysical and optoelectronic properties of certain hybrid materials. Resting at a crossroad between molecules and solid-state materials, research on organic-inorganic materials involved principles borrowed from both chemistry and physics. Specifically, in contrast to conventional wisdom, the project team investigated how the addition of point defects in hybrid halide perovskites can be used to enhance the efficiency of the photoconversion process in photovoltaics. Results helped scientists better comprehend the role of chlorine dopants and organic cations in suppressing carrier recombination and restoring long-lived charge carriers. From 2D materials to heterostructures With several 2D materials at hand, scientists concentrated on combining them in vertical stacks. The design of multilayer architectures based on ultra-thin 2D material building blocks was assisted by advanced solution processing techniques. Organic molecules aided in the liquid exfoliation process by delaminating materials into individual, ultra-thin, and importantly, stable sheets. “Constructing stable conjugated polymers was key to studying the powerful tuning mechanisms of the electronic and optical properties of elementary 2D units,” points out Beljonne. Amongst other findings, the project team demonstrated that the electrical properties of metal dichalcogenide 2D layers can be tuned by ion bombardment and that the resulting sulphur vacancies act as favourable anchoring groups for thiol-based multifunctional molecules. Stacked 2D materials possess an array of tuneable properties that are expected to be important for future applications in electronics and optoelectronics. Possible applications range from microchip components to thin and flexible solar panels and display screens. This project work has also led to further studies on other 2D material systems. DEMONH contributed to a better fundamental understanding of the complex electronic and optical properties of certain semiconductor and hybrid materials. This will hopefully guide the design and development of next-generation ultra-thin and flexible multilayer heterostructure devices.
Keywords
DEMONH, electronic, 2D materials, optical properties, hybrid materials, optoelectronic, graphene, conjugated polymers, multilayer heterostructure
