Intercalation-Exfoliation of MoS₂ with Evaporable Stabilizer to Obtain High-Yield Monolayers Inks for Printable Photodetectors

Photodetectors are electronic devices which convert light into an electrical signal. Printable, flexible and low-cost photodetectors are in high demand as these devices can be used in a variety of applications such as cameras for smartphones, medical sensors, night vision or even ambient light sensors.<br/>Transition Metal Dichalcogenides (TMDs) possess strong light emission and absorption in the visible and near-infrared wavelength range, making them very attractive materials for optoelectronic applications. Molybdenum disulfide (MoS₂) is a multilayer 2D material that can be exfoliated to obtain monolayers, this material is also characterized by multiple crystalline phases. With this variety of structures, it is possible to adjust the band gap of MoS₂ from an indirect band gap at 1.29eV to a direct band gap at 1.8eV. Moreover, metallic or semi-conductor monolayers can also be obtained.<br/>Chemical vapor deposition can be used to produce semi-conductor monolayer TMDs with controllable synthesis. However, large scale, and low-cost production is very difficult with this technique. Intercalation followed by liquid-phase exfoliation is a powerful technique to produce defect-free monolayers in large-quantities. However, reproducible printable inks with high concentration of TMD monolayers are more difficult to achieved. Another challenge to obtaining good quality TMD inks for printable photodetectors is the necessary to use a large amount of insulating stabilizer (such as PVP or ethyl cellulose).<br/>Our work focuses on the development of highly concentrated MoS₂ inks for printable photodetectors. This ink was made by a new intercalation-exfoliation process, an easily evaporable stabilizer was used to replace PVP, and a cascade centrifugation step was added to the process to achieve a highly efficient monolayer size selection (90% of the flakes have less than 3 layers).