Scientists have calculated that the total solar energy hitting the earth's surface is more than 5000 times greater than the current energy demand of mankind. Harnessing this gigantic surplus of energy is what drives Professor Thomas Hannappel. The head of the "Fundamentals of Energy Materials" department at TU Ilmenau and winner of the 2022 Thuringian Research Award is researching, among other things, how to increase the efficiency of conventional solar cells more and more - for example, with innovative semiconductors that absorb solar radiation and convert it into electrical power. The stacked, multiple and tandem solar cells optimized by Hannappel and his team are already much more energy-efficient than previous solar cells.

Let there be light!

According to Hannappel, tandem structures in particular hold highly effective potential. With just a single component, i.e. without the detour via a normally required electrolyzer, water can be broken down into its components oxygen and hydrogen. And quite a few people see (green) hydrogen as the energy carrier of the future, which could gradually replace fossil fuels - if it is produced from renewable sources. In specialist circles, such a stand-alone component, which does not require any external wiring, is also referred to as an "artificial leaf" - based on nature, which also operates tiny power plants with a single "component", the green leaves of plants. Powered solely by sunlight and water, they use photosynthesis to convert carbon dioxide from the atmosphere into energy sources such as sugar. And it is precisely this principle of nature that underlies the idea of Professor Hannappel and his team: a kind of artificial photosynthesis for direct solar fuel generation.

A big dream

The possible goal at the end of this effort: Fuel in abundance, cheap and clean. "If I'm allowed to dream as a scientist, with artificial photosynthesis we'll push open the door to a world where green energy sources are critical to the reliability of our energy system, great mobility and stable energy storage," Hannappel said.

No one is an island

He is also receiving support from the German Federal Ministry of Education and Research, which has launched the DEPECOR ("Direct Efficient Photoelectrochemical CO2 Reduction") project for this purpose. Coordinated by the Technical University of Ilmenau, top-class international partners from science and industry are working on the above-mentioned goal. On the German side, these include the TU Munich, the Helmholtz Center for Materials and Energy Berlin, the Fraunhofer Institute for Solar Energy Systems and Azur Space Solar Power GmbH - as well as the renowned California Institute of Technology (Caltech) in Pasadena as an associated partner.

And it works!

In fact, this research community can already demonstrate success. For example, the team has now succeeded in setting a new record for the conversion of carbon dioxide into usable fuels in a stand-alone, solar-powered device. The efficiency of over five percent with a stability of more than 50 hours shows that the innovative, complex process can indeed produce high-quality fuels from CO2: Ethanol, carbon monoxide and methanoic acid. Hannappel recently published the results of his research in the renowned scientific journal "Advanced Energy Materials".

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