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Iridium - The new “gold“ for high-temperature nanophotonics

In a notable development that could reshape the landscape of energy harvesting and renewable power generation, a collaborative team of scientists from the DFG’s SFB 986 project belonging to Helmholtz-Zentrum Hereon and Hamburg University of Technology in cooperation with Aalborg University has reached a significant milestone in the field of thermophotovoltaics (TPV). The team has successfully designed and experimentally validated oxidation-resistant iridium-based metamaterials for selective emitters, offering new possibilities for highly efficient energy conversion from heat to electricity.

Thermophotovoltaics, a promising technology that enables the direct conversion of heat radiation into electricity, has gained attention as a potential solution for clean and efficient power generation. The success of this technology largely hinges on the performance of selective emitters that absorb heat as the primary energy source and emit tailored radiation at near-infrared wavelengths of light while minimizing heat loss by suppressing long wavelength radiations. To achieve this spectral selectivity, metals have to be nanostructured into so called metamaterials (as seen in Fig. 1). Until now, the challenge of fast metal oxidation above 800 °C has hindered the practical implementation of such metamaterials for thermophotovoltaic systems.

Fig. 1. The image on left shows a cross-sectional transmission electron microscope image of the metamaterial emitter with distinct iridium and hafnia nanolayers. The image on the right shows the selective emitter at 1000 °C in an in-situ x-ray diffraction annealing chamber.

The multidisciplinary team from diverse fields has overcome this obstacle by developing oxidation-resistant iridium-based selective emitters. Iridium, known for its exceptional oxidation resistance at high temperatures, has been tailored at the nanoscale using magnetron sputtering to exhibit unique optical properties, making it a promising candidate for selective emitters in TPV applications.

"With iridium, we address both aspects at the same time: spectral selectivity and thermal stability," says Alexander Petrov, who works on optical properties of materials at TUHH. "Selective emitters based on iridium are very good at suppressing unwanted radiation and do not react with oxygen. Iridium is a precious metal like gold, but suitable for high-temperature applications."

"By avoiding the adverse effects of oxidation, we have unlocked the potential for more efficient and sustainable systems." reports Gnanavel Vaidhyanathan Krishnamurthy, lead author of the study and a scientist at the Helmholtz-Zentrum Hereon. "This innovation opens the doors to new possibilities in waste heat recovery, solar thermal power generation and beyond."

The key highlight of this work include: experimentally demonstrating the thermal stability of the selective emitter at 1000 °C for 100 h at technical vacuum conditions by state-of-the-art in-situ x-ray diffraction facilities. The results of the current work align with global efforts to transition towards cleaner and more sustainable energy sources, contributing to reducing greenhouse gas emissions and dependence on fossil fuels.

The research work is part of the Collaborative Research Centre SFB 986, which deals with tailor-made multiscale material systems.



Krishnamurthy, G. V., Chirumamilla, M., Krekeler, T., Ritter, M., Raudsepp, R., Schieda, M., Klassen, T., Pedersen, K., Petrov, A. Yu., Eich, M., Störmer, M., Iridium Based Selective Emitters for Thermophotovoltaic Applications. Adv. Mater. 2023, 2305922. https://doi.org/10.1002/adma.202305922



Dr. habil. Alexander Petrov

Institute of Optical and Electronic Materials, TUHH



Prof. Dr. Manfred Eich

Institute of Optical and Electronic Materials, TUHH



Dr. Michael Störmer

Institute of functional materials for sustainability, Helmholtz-Zentrum Hereon