A Scalable Route for Composition-Tunable Transition Metal Dichalcogenide Nanosheets

The alloying of 2D TMDs is an established route to robust semiconductors with continuously-tunable optoelectronic properties. However, a major obstacle in commercializing large-area, thin devices based on alloyed TMD nanosheets is their large-scale production.¹<br/><br/>In this presentation we describe major advances that address this issue. Firstly, we describe a new powder-based, solution processable method to produce high quality 2D TMD nanosheets using a pre-annealing step and electrochemical intercalation/exfoliation.² Compared to traditional methods (i.e., ultrasonication), 2D TMD nanosheets produced using our method show ameliorated optoelectronic properties owing to high aspect ratios and low defect densities. Next, we demonstrate how this innovative method can be adapted to afford production of ternary (Mo_0.5W_0.5S₂, Mo_0.5W_0.5Se₂, MoSSe, WSSe) and quaternary (Mo_0.5W_0.5SSe) alloyed TMD nanosheets from commercially available, pure-phase bulk TMD powders. We provide evidence of the atomic mixing within the nanosheets using atomic resolution scanning transmission electron microscopy (STEM) in combination with integrated differential phase contrast (iDPC) for the metal and chalcogenide atoms, respectively. Furthermore, we show that control over the final composition of the nanosheets can be exerted by tuning the feed ratios of the TMD powders. Accordingly, we examine the unique optoelectronic properties that arise as a function of the chemical composition of the alloy. Notably, the phenomena observed are consistent with nanosheets produced <i>via </i>chemical vapor deposition (CVD) and related methods, suggesting that this versatile method is an economically viable solution for making alloyed 2D TMD nanosheets. Indeed, the ability to produce controllably alloyed TMD nanosheets in large quantities is critical for the inexpensive production of next-generation, large-area optoelectronic devices.<br/><br/>In order to transform our exfoliated materials into large-area, thin films, we report the further advancement of our preparation methods toward a continuous roll-to-roll deposition of TMD-based thin films from nanosheet dispersions using a liquid-liquid self-assembly technique.³ We demonstrate reproducible printing of 100mm wide TMD nanosheet films on plastic substrates. Thus, the advances presented here represent a comprehensive route towards large-area, tunable, and fully solution-processable 2D TMD-based devices.<br/><br/>[1] Wells, R.A.; Sivula, K. Assembling a Photoactive 2D Puzzle: From Bulk Powder to Large-Area Films of Semiconducting Transition-Metal Dichalcogenide Nanosheets. <i>Accounts of Materials Research.</i> <b>2023</b> <i>4</i> (4), 348-358. DOI: 10.1021/accountsmr.2c00209<br/><br/>[2] Wells, R.A.; Diercks, N.J.; Boureau, V.; Wang, Z.; Zhao, Y.; Nussbaum, S.; Esteve, M.; Caretti, M.; Johnson, H.; Kis, A.; Sivula, K. Composition-Tunable Transition Metal Dichalcogenide Nanosheets via a Scalable, Solution-Processable Method. <i>(Submitted) </i><b>2023.</b><br/><br/>[3] Wells, R. A.; Johnson, H.; Lhermitte, C. R.; Kinge, S.; Sivula, K. Roll-to-Roll Deposition of Semiconducting 2D Nanoflake Films of Transition Metal Dichalcogenides for Optoelectronic Applications. <i>ACS Appl. Nano Mater.</i> <b>2019</b>, <i>2</i> (12), 7705–7712. https://doi.org/10.1021/acsanm.9b01774.