Sven Burger, Bernd Rech
Felix Binkowski (ZIB)
01.01.2019 – 31.12.2021
The energy supply network needs to go through tremendous change in order to meet the demands to mitigate climate change. To achieve this, every aspect of the supply chain must be carefully evaluated and optimized. A cornerstone of any sustainable energy network will be solar energy. While conventional solar cells are rapidly increasing their penetration into energy markets, the requirement of electricity networks to provide on demand power is at odds with the intermittent supply of solar cells.
Solar fuel devices are able to convert solar energy directly into usable fuels, thus storing the energy and allowing distribution through existent networks. Of the various fuels which can be created using photo-chemistry, hydrogen, obtained from water splitting, is the most prominent candidate due to the abundant, low-cost supply of water. Therefore, a better understanding of solar-driven water splitting and developing the technology for water splitting on a large scale is a central challenge facing the transition to a green economy.
Optical device design is an important problem for both of these technology steps: One of the limitations of both currently available PV technology and the developing solar fuel technologies is insufficient absorption of light due to reflective losses, transmissive losses and parasitic absorption. In order to overcome these challenges, optical modelling will play a crucial role. Proper light management in many photovoltaic devices has already lead to large increases in efficiency, typically through the use of periodic nanostructures. However, there exist multiple areas for which current models are insufficient. Amongst many others, specifically, efficient, rigorous models for isolated scatterers and for isolated sources in periodic media are needed.
This project develops and investigates rigorous methods to treat light scattering problems, especially also problems including isolated sources and scatterers in periodic media. Further the developed methods are applied to investigate multiscale effects in topical energy storage and photochemistry devices and to optimize their performance, in direct collaboration with physicists, chemists and engineers of Helmholtz Zentrum Berlin für Energie und Materialien (HZB) and with external collaboration partners.
Isolated sources appear, e.g., in quantum dot upconversion materials which are combined with periodic nanostructures. In order to simulate light scattering of isolated sources in such environments we use high-order FEM to simulate Maxwell’s equations in a subtraction field formulation. Localized sources are modeled here as periodic dipole sources. In order to build a non-periodic model of the source in the periodic medium, a summation is performed where the phase of the emitted field is varied over the Brillouin zone. A regular, cartesian sampling of this phase distribution has been shown to be inefficient as it requires too many fields before it converges, due to typically present singularities in Bloch space. Therefore cartesian sampling results in too large computation times. We develop adaptive approaches for sampling the Brillouin zone.
First research results of this project include application of theoretical models for light matter interaction [1, 2, 3] to surface chemistry and photocatalysis [4, 5], as well as optimizations for energy-efficient light emitting devices  and for photonic upconversion devices . The images below show visualizations of field distributions in nanoscale devices some of which are realized experimentally at HZB.
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