Novel exfoliation method paves the way for printable optoelectronic devices

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A team of scientists from the National University of Singapore (NUS) has successfully developed an improved method of producing molybdenum disulphide crystals for use in printable optoelectronic devices. The process, which has been published in January’s edition of journal Nature Communications, produces the crystals with a higher yield and higher flake size than existing methods.

The fast growing field of printed photonics, electronics and optoelectronics demands high material quality, precise material deposition, and application-specific optical, electrical, chemical, and mechanical properties.

The molybdenum disulphide crystals are a class of chalcogenide compounds. Transition metal dichalcogenides have recently attracted a high level of attention as the next generation of two-dimensional materials due to their electronic and optical properties, for applications in optoelectronic devices such as thin film solars, photodetectors flexible logic circuits and sensors.

However, current processes of producing printable single layer chalcogenides take a long time and the yield is poor. The flakes produced are of submicron sizes, which make it challenging to isolate a single sheet for making electronic devices.

Using a two-step expansion and intercalation method, the researchers were able to produce high quality single-layer molybdenum disulphide sheets with unprecedentedly large flake size. The team also demonstrated that the good dispersion and high viscosity of the flakes render it highly suitable for inkjet printing.

‘At present, there is a bottleneck in the development of solution-processed two dimensional chalcogenides. This new method is more efficient than previous solution-based methods,’ said Professor Loh Kian Ping, who led the project and heads the Department of Chemistry at the NUS Faculty of Science.

To further their research and to cater for the growing demand in industry, the team will be looking at developing inks based on different types of two-dimensional chalcogenides produced by the same method, in order to produce printable optoelectronic devices. They will also be testing the optical properties of the flakes they have produced.