Non-Technical: Two dimensional semiconductors show great promise for optoelectronic applications, due to a myriad of highly attractive properties, however, to date they have shown tremendously poor photoluminescence quantum yield. High quantum yield is a requirement for materials used in optoelectronic devices such as light emitting diodes, lasers, and solar cells. This EAGER project addresses the quantum yield issue of transition metal chalcogenides (2D material). The PI has demonstrated that the surface defects of MoS2 (2D material) can be repaired/passivated through surface chemical treatments. As a result; the quantum yield can be enhanced from less than 1% to over 95%. The work outlined in this EAGER will seek to demonstrate a functional electro-optic device based on a high quantum yield 2D monolayer.
The figure of merit for materials used in optoelectronic systems is their photoluminescence quantum yield (QY). This determines the efficiency of light emission from a population of optically or electrically generated electron hole-pairs and is critically dependent on the defect density/type in the material. Final QY values dictate key performance metrics such as the power consumption in LEDs, threshold currents for semiconductor laser, and the upper limit of open circuit voltage in solar cells. Two dimensional (2D) semiconductors, suffers from very poor quantum yield (<1%). Recently the PI?s group has addressed this problem of low QY in 2D materials and developed a chemical treatment procedure using an organic super acid which is able to enhance the QY in the most heavily studied 2D system: MoS2 from an initial value <1% in the as exfoliated case to over 95%. This work shows that the procedure is stable in ambient and does not change other key properties in the material (such as crystal structure, band gap, electrical properties, etc.). The detailed mechanism of the treatment need to be fully understood for this result to realize its full impact. The PI will address many of these key questions, focusing on: (i) obtaining high QY for additional 2D materials such as WS2, and ReS2 via exploring and optimizing additional chemicals and optimizing the existing treatment procedure for different materials. The demonstration of an optoelectronic device using this technology, specifically a 2D LED, with a high QY will be demonstrated. This project will involve one graduate and one undergraduate student; the training and mentoring of the undergraduate student in particular will be emphasized. The nature of the proposed work is interdisciplinary and spans the fields of chemistry, materials science, and device fabrication.
