Semiconducting two dimensional transition metal dichalcogenides via solution-processable routes

Two-dimensional (2D) transition metal dichalcogenides (TMDs) possess remarkable optoelectronic properties which are unique and tunable based on composition and thickness. These materials are posed to revolutionize ultrathin devices across many fields including transistors, light emitting diodes, solar cells, and photoelectrodes, to name a few. In particular, single-flake devices for solar energy conversion have achieved promising performances using high-quality TMD nanosheets. However, a major obstacle to realizing these devices outside of the lab continues to be the large-scale production of pristine 2D TMD nanomaterial. To this end the following work aims to overcome the issue of scalability to produce thin films of semiconducting 2D TMD nanosheets without sacrificing material quality nor device performance. The first chapter lays a road map of how to reach this goal and highlights issues that will be addressed. The second chapter details the development of a novel powder-based electrochemical pellet intercalation (ECPI) technique which allows for scalable production of solution-processable 2D TMDs. Using this technique to prepare 2D MoS2 yields extremely thin semiconducting nanosheets (predominantly monolayers) with large lateral dimensions (> 1µm) and impressive absorbed photon-to-current conversion efficiencies (APCE) up to 90%, suggesting high quantum yield. Notably this method can be used to make a range of 2D TMDs including MoS2, WS2, and WSe2. In the third chapter the ECPI method is further extended to produce alloyed 2D TMD nanosheets, which allows for continuous tuning of their optoelectronic properties. In addition to compositional tuning, five alloys, four ternary (Mo0.5W0.5S2, Mo0.5W0.5Se2, MoSSe, WSSe) and one quaternary (Mo0.5W0.5SSe), are demonstrat-ed. This demonstration greatly expands the range of optoelectronic properties that can be obtained via economic and solution-processable means and leads the way to large-area 2D TMD devices. Finally, chapter four describes a method for processing large volumes of TMD nanosheets into large-area films without compromising favorable film morphology. The method is developed into a continuous roll-to-toll (R2R) film system, capable of printing ultrathin TMD films at the meters-squared scale. In addition to being applicable to different 2D TMDs (MoS2 and WSe2), it is also viable for the production of large-area heterojunction thin films. Together these chapters address multiple key challenges in the field and present a holistic approach to overcoming them.