May 10, 2022
First principles investigation of the effect of excess carriers and illumination on the band edge energies of semiconducting transition metal dichalcogenides
Abstract
Photovoltage, or the change in surface potential of a material under illumination, is a central quantity for characterizing complex semiconductors and for optoelectronic applications such as photocatalysis. In this seminar, I will discuss first principles calculations to understand two of the key components of photovoltage in the limit of well-defined semiconducting two-dimensional transition metal dichalcogenides (TMDs), materials with strong light-matter interactions that have been reported to be photocatalytically active. Under operating conditions, the absolute band edge positions of photocatalysts are altered due to the presence of optically excited electrons and holes and, often, excess electrons or holes due to gating. These two effects are relevant to setting limits on experimentally realizable photovoltages and are generally neglected in calculations of the band edge energies of photocatalysts. By modeling the effect of excess free carriers using density functional theory (DFT), shifts in the absolute band edge energies are computed as a function of carrier density. Additionally, using DFT calculations in conjunction with ab initio many-body perturbation theory calculations using the time-dependent adiabatic GW-Bethe-Salpeter equation approach, we explore the effects of illumination on the band edges as a function of pump energy, profile, and intensity.
Elizabeth Peterson is a PhD candidate in the Physics Department at UC Berkeley. She received her Bachelors of Science degrees in Chemistry and Applied Mathematics at UCLA in 2013. Her undergraduate research studies involved developing algorithms to analyze MRI data for early tumor detection. From 2014-2016 she worked at StitchLabs, Inc., a tech start-up in San Francisco that made inventory management software for ecommerce sellers, where she worked in tech support and data analysis. She began her PhD studies at UC Berkeley in 2016. In 2021 Elizabeth was awarded the Kavli Energy NanoSciences Institute's Philomathia Graduate Student Fellowship. Her research interests include using first-principles computational condensed matter techniques to study 2D materials and metal oxides for applications in artificial photosynthesis and valleytronics technology. In her spare time, Elizabeth enjoys distance running, reading the New Yorker, watching history documentaries, and eating lots of sushi.