Layered and Two-Dimensional Transition Metal Dichalcogenide Devices for Flexible Electronics and Energy Harvesting

• Applicant: Professor Dr. Alwin Stefan Daus
• Subject Area: Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 506140715

Emerging two-dimensional and layered transition metal dichalcogenides (TMDs) are promising for flexible electronics. However, they cannot unleash their true potential until device engineering challenges and large-area synthesis have been addressed. Here, I will focus on tungsten diselenide (WSe2) and molybdenum diselenide (MoSe2) which have distinct advantages for transistors and solar cells. They can be used as n-type and p-type semiconductors enabling complementary metal-oxide semiconductor (CMOS) electronics, long sought after in flexible electronics. For solar cells, WSe2 and MoSe2 offer ideal band gaps for sunlight harvesting and ultra-high absorption coefficients allowing for extreme light-weightiness.At RWTH Aachen, I aim to develop scalable synthesis of WSe2 and MoSe2 where I have access to new cutting-edge growth equipment specialized for TMDs and strong support through the Aachen Graphene & 2D Materials Center. I will use selenization of metal precursor thin-films with varying thicknesses from ~1-100 nm covering the ranges needed for transistors and solar cells with the goal to achieve excellent electronic quality i.e., carrier mobility ≥20 cm2V-1s-1. I will add metal impurities to the precursor films to enhance doping and crystallinity aiming to form pn-junctions and compare them with WSe2-MoSe2 heterojunctions. I will analyze growth uniformity on 4” wafer scale.I will conduct intensive studies on contact metals and metal-oxide interlayers for both transistors and solar cells. Metal-oxide interlayers can help to control switching properties of transistors and improve carrier extraction in solar cells important for a higher power conversion efficiency (PCE).I will fabricate flexible devices with a previously developed transfer technique and refine it further for low-voltage transistors with radio frequency operation. I will form small CMOS circuits and analyze performance and energy efficiency, which together with statistics on large-area parameter distributions will allow evaluating prospects for future circuits and systems. Flexible solar cells will be realized with the goal of PCE ≥16% achieved by abovementioned contact engineering, pn-(hetero)junctions and optical design. With minimized material/substrate thicknesses, I aim for a record power-per-weight of ≥35 Wg-1. Successively, the area of such solar cells will be scaled up to square-cm carefully considering thin-film integrity, device yield and design changes. This project is intended to lay the foundation for a TMD technology for flexible electronics. I believe that together with future TMD memory and sensors the way for flexible all-TMD IoT systems can be paved. Furthermore, TMD solar cells have strong potential for weight-sensitive fields such as aerospace, electric cars, architecture or wearables.

• DFG Programme: Independent Junior Research Groups