Next 15 of July 2025 we will have an invited seminar by Dr Urs Aeberhard on Advanced Simulation for Tandem Photovoltaics. It will be held at room B223, ETSI de Telecomunicación, Building B, at 14:30.
Urs Aeberhard received his PhD in theoretical solid state physics from ETH Zürich (Switzerland) in 2008, for a thesis on a microscopic theory of quantum well solar cells, performed in the Condensed Matter Theory group at Paul Scherrer Institute (PSI). From 2009-2018, he was a postdoc, senior scientist, and tenured group leader at the Institute of Energy and Climate Research – Photovoltaics IEK-5 (now: IMD-3), Forschungszentrum Jülich (Germany), heading the activities in Theory & Multiscale Simulation. In 2013, he spent half a year as a visiting research scholar at the National Renewable Energy Lab (NREL) in Golden, Colorado (USA). In 2018, he joined the company Fluxim based in Winterthur (Switzerland) as a Senior R&D Scientist to perform model development and applied research for emerging opto-electronics. Since 2019, he is also a Guest Lecturer for the simulation of photovoltaic devices at ETH Zürich. Dr. Aeberhard is the developer of pioneering quantum-mechanical simulation approaches for nanostructure-based solar cells and the author of numerous publications on this topic.
This is an abstract of Dr Aeberhard's talk.
Multi-junction solar cells that combine absorbers of varying band gaps to enhance the utilization of the broadband solar spectrum by reducing transmission and thermalization loss represent the highest efficient photovoltaic devices and a vastly successful implementation of a concept aiming at power conversion efficiencies beyond the single junction detailed balance limit. However, the ultra-high efficiencies come at the cost of increased complexity, not only in the device layout, where stacks with a large number of different layers dominate, but also in operation.
Especially in the domain of monolithically integrated two-terminal devices, where the sub-cells are connected in series, the stack layout needs to be designed carefully in order to balance the currents at the relevant point of operation, which is usually the maximum power point. This then regards not only the photocurrent, but also the currents due to recombination of electrically or optically injected charge carriers. In the material systems that are often used for top cells, such as III-V semiconductors or metal-halide perovskites, the high radiative efficiencies and steep absorption edges promote contributions from re-absorption of internally emitted photons in the form of additional generation due to photon recycling and luminescent coupling. The recombination, on the other hand, is affected by the details of charge transport in the actual device configuration, such as mobilities of charge carriers and the presence of extraction barriers, which can also be affected by the device operation, as internal fields vary under bias voltage or due to the impact of mobile ions. Further complexities arise from the requirement of an efficient recombination contact and the presence of reverse-bias conditions on sub-cells at moderate external voltages or under strong mismatch of sub-cell photocurrents. In this situation, detailed numerical simulation of solar cell operation can support the design, analysis and optimization of the photovoltaic device architectures.
In my presentation, I discuss our recent efforts [1-3] towards a versatile numerical simulation tool suited for supporting research and development in the field of tandem photovoltaics. I will introduce first the general challenges of opto-electronic tandem device design and then discuss some specific aspects of the optical and electrical models proposed, such as our recently developed approach for photon recycling and luminescent coupling, models for recombination junctions in different tandems, and the simulation of reverse-bias breakdown in tandems and how to consider there influence of mobile ions in perovskite sub-cells.
[1] S.J. Zeder, B. Blülle, B. Ruhstaller, U. Aeberhard, “Optimizing perovskite LEDs and tandem PV cells: The role of photon-recycling and luminescent coupling in presence of strong light scattering”, APL Energy 3, 026110 (2025).
[2] U Aeberhard, N Natsch, A Schneider, S. J. Zeder, H. Carrillo-Nuñez, B. Blülle, B. Ruhstaller, “Multi-Scale Simulation of Reverse-Bias Breakdown in All-Perovskite Tandem Photovoltaic Modules under Partial Shading Conditions”, Solar RRL 8, 2400492 (2024).
[3] U. Aeberhard, S. J. Zeder, B. Ruhstaller, “Effects of Photon Recycling and Luminescent Coupling in All‐Perovskite Tandem Solar Cells Assessed by Full Opto‐Electronic Simulation”, Solar RRL 8, 2400264 (2024).
