Periodic Reporting for period 2 - PhotoNow (Discovery and Characterization of Third-Generation Nonlinear Photovoltaics)
Berichtszeitraum: 2022-12-01 bis 2024-05-31
The main topic addressed in PhotoNow deals with the nonlinear absorption of light by materials. Nonlinear absorption means going beyond the standard photovoltaic effect that is linear in the electric field of light and considering secondary contributions that are often more subtle. This is important as it increases our knowledge on the way materials absorb the solar spectrum and might therefore help us propose alternative ways to extract solar energy in the future. Alongside, it also allows us to learn more about the electronic properties of different types of materials, using light as a probe. This includes novel materials such as nearly two-dimensional thin films made of transition metal-dichalcogenides or so-called Weyl semimetals that have a strong connection to topological physics.
The main question we try to answer in PhotoNow is how large is the nonlinear light-absorption process in comparison to the standard photovoltaic effect and in which materials (if any) can it surpass the standard absorption. While the standard photovoltaic effect has been thoroughly studied over the years and is widely employed in current solar-cell devices, the nonlinear contribution is comparatively much less understood. PhotoNow aims at an improved understanding of the various effects that build up the nonlinear material response to light. We employ two main tools to achieve this purpose; theoretical derivations and computational calculations. The former allow us to deepen our fundamental understanding of the interaction between light and the electrons present in a material. Once we obtain a theoretical picture of the process, it is time to let the machines use their ability to perform complex numerical calculations that then allow us to perform quantitative predictions about the light-absorption capabilities of concrete materials. For such purpose, we often develop computational programs that we then share with the scientific community as free-software tools.
The main question we try to answer in PhotoNow is how large is the nonlinear light-absorption process in comparison to the standard photovoltaic effect and in which materials (if any) can it surpass the standard absorption. While the standard photovoltaic effect has been thoroughly studied over the years and is widely employed in current solar-cell devices, the nonlinear contribution is comparatively much less understood. PhotoNow aims at an improved understanding of the various effects that build up the nonlinear material response to light. We employ two main tools to achieve this purpose; theoretical derivations and computational calculations. The former allow us to deepen our fundamental understanding of the interaction between light and the electrons present in a material. Once we obtain a theoretical picture of the process, it is time to let the machines use their ability to perform complex numerical calculations that then allow us to perform quantitative predictions about the light-absorption capabilities of concrete materials. For such purpose, we often develop computational programs that we then share with the scientific community as free-software tools.
We have worked in several theoretical and material fronts. One the one hand, we have developed a combined theoretical and computational scheme that allows an accurate numerical assessment of the nonlinear optical properties of materials. In particular, we have modeled third-order electric field effects as well as so-called many-body corrections that offer an improved description of the light-matter interaction and go beyond the state-of-the-art in several aspects. In addition, this work has crystallized in a free-software package that researchers in the scientific community can employ for their own investigations.
Alongside the methodological developments described above, we have thoroughly worked on applying the combined theoretical and computational scheme to several types of materials. On one hand, we have studied a concrete Weyl semimetal, namely TaIrTe4. This compound has attracted recent interest as it exhibits an unusually large nonlinear optical absorption as measured in experiment, and is therefore considered a potential candidate for optical applications. By applying our scheme, we have been able to discern which of the various nonlinear effects at play is the dominant one, which turns out to be the so-called jerk current. Secondly, we have performed numerical calculations to describe the nonlinear optical properties of a particular nanomaterial, namely a WS2 nanotube. Nanotubes are formed by stacks of monolayers rolled into tube form, therefore offering an interesting bridge between a purely two-dimensional and a common three-dimensional material. Our calculations have shown that the quadratic optical effect known as the shift current is enhanced in nanotubes due to a combination of innate ability to absorb light and favorable geometric aspects such as large cross-sectional area to drive the generated photocurrent along the tube axis.
Alongside the methodological developments described above, we have thoroughly worked on applying the combined theoretical and computational scheme to several types of materials. On one hand, we have studied a concrete Weyl semimetal, namely TaIrTe4. This compound has attracted recent interest as it exhibits an unusually large nonlinear optical absorption as measured in experiment, and is therefore considered a potential candidate for optical applications. By applying our scheme, we have been able to discern which of the various nonlinear effects at play is the dominant one, which turns out to be the so-called jerk current. Secondly, we have performed numerical calculations to describe the nonlinear optical properties of a particular nanomaterial, namely a WS2 nanotube. Nanotubes are formed by stacks of monolayers rolled into tube form, therefore offering an interesting bridge between a purely two-dimensional and a common three-dimensional material. Our calculations have shown that the quadratic optical effect known as the shift current is enhanced in nanotubes due to a combination of innate ability to absorb light and favorable geometric aspects such as large cross-sectional area to drive the generated photocurrent along the tube axis.
We have gained insight into the role of nonlinear optical processes in materials of current interest like Weyl semimetals and transition metal dichalcogenide nanotubes, and we have also deepened our knowledge on the topological aspect of nonlinear responses. In performing these tasks, we have developed computational algorithms that allow the calculation of nonlinear optical properties with great accuracy.
In the future, we expect to extend our analysis to situations where the external optical field is periodic in time, making use of the so-called Floquet formalism. In addition, we expect to incorporate magnetic compounds to our pool of materials and discern the particular features that magnetism brings into play in nonlinear optics.
In the future, we expect to extend our analysis to situations where the external optical field is periodic in time, making use of the so-called Floquet formalism. In addition, we expect to incorporate magnetic compounds to our pool of materials and discern the particular features that magnetism brings into play in nonlinear optics.