e-conversion Cluster of Excellence: basic research for the energy transition

Enlarge

Over a third of the global electricity mix now comes from renewable energy sources – and the trend is upward, especially when it comes to solar energy. Almost a seventh of the global demand for primary energy is covered by renewables. The outlook was a lot bleaker just a few short years ago.

Nevertheless, we need to dramatically reduce our use of fossil fuels and replace them with renewables to curtail the climate crisis. Yet demand for electricity is set to further increase over the coming years: e-mobility, for example, will continue its rise, while the global boom that has begun in artificial intelligence will cause the electricity demand of computers to explode. With current technologies alone, we will not be able to solve the problems – that much is certain.

This is the global backdrop to the efforts of Frédéric Laquai and Achim Hartschuh, who work on fundamental questions of energy conversion and on finding intelligent and sustainable solutions for photovoltaics, catalytic techniques, and batteries that could make the energy transition possible. The two LMU scientists are professors of physical chemistry and spokespersons for the e-conversion Cluster of Excellence, which is now entering its second phase. Until recently, Hartschuh was the LMU representative on the spokesperson panel for the large research alliance, which the Technical University of Munich and LMU are jointly managing. For the next few years, Laquai, an expert in the spectroscopy of energy materials, will be taking over Hartschuh’s role. Meanwhile, the TUM representatives for the new phase will be Jennifer Rupp, Professor of Solid-State Electrolyte Chemistry, and Ian Sharp, Professor of Experimental Semiconductor Physics. The team of spokespersons also includes Bettina Lotsch, Professor of Chemistry and Director at the Max Planck Institute for Solid State Research in Stuttgart.

The Max Planck Institute for Solid State Research, the Fritz Haber Institute of the Max Planck Society, and the Deutsches Museum in Munich are also participating in the cluster in addition to the two Munich universities. In total, some 40 principal investigators and their research groups are collaborating on the large-scale undertaking. They bring together a wide variety of expertise, from nanoscience and quantum research, to semiconductor physics and materials science, to computational science and artificial intelligence. The alliance is based not least on the findings of the Nanosystems Initiative Munich, one of the original clusters of excellence. On top of this, the cluster is further expanding its global cooperation network with the addition of relevant research centers, including from the Global South.

“Going beyond our current energy scenario”

The shared goal is to develop sustainable concepts for energy conversion and storage and new materials and systems. The work of e-conversion thus strives to “go beyond our current energy scenario.” A major part of the energy transition still relies on a small number of concepts, which in turn are based on just a handful of materials, “many of which are problematic or unsustainable.”

No shortage of challenges, then. The Cluster of Excellence sees itself as an innovation platform and pursues a broadly interdisciplinary “horizontal” approach, with a clear focus on basic research. For Hartschuh and Laquai, this is precisely the view from above that is required not only to explore individual technologies, but also to identify viable new approaches. “We’re not in the business of delivering fast solutions. But our fundamental research is aimed at energy technologies that shape the future,” says Laquai.

Hartschuh uses an example to illustrate the synergies which the wide-ranging concept can unlock. Just recently, two teams from LMU and TUM developed a particularly effective absorber, a sort of synthetic light trap. The device is designed to help improve photocatalytic applications in which light is converted into chemical energy. That they also employed DNA origami for this light antenna in order to build a suitable 3D structure out of DNA material on a nanoscale – nobody would have dreamed of doing that with a silo mentality, reckons Hartschuh.

What goes on at interfaces

In the view of Hartschuh and Laquai, the most compelling reason for the synergistic approach is the following: Although there are substantially different material classes in energy research, the fundamental mechanisms are very similar. For example, the processes of energy conversion, the separation of charge carriers, and the transport of ions often take place at interfaces – whether in batteries or photovoltaic cells. To understand what happens at such boundary surfaces, why things like recombination losses, resistances, and other limitations can occur there, and how excitation and energy conversion processes might be controlled better – this requires delving into the atomic details.

To better understand the complex processes, the researchers in the cluster started by studying model systems. In the second phase, which is now beginning, they plan to investigate “more realistic energy systems” in detail. To this end, they developed a whole suite of instruments – high-resolution and ultrafast microscopic and spectroscopic techniques – during the first funding period in order to observe the model systems at work, as it were, and thus gain a better understanding of them. Now they plan to refine this arsenal of methods in specific ways.

The search for suitable materials also remains on the agenda for e-conversion. In photovoltaics, for instance, the widely used semiconductor material silicon cannot “go beyond 30 percent efficiency due to its physical characteristics,” explains Laquai. By contrast, so-called tandem solar cells, which use a combination of different materials for more efficient light conversion, “can achieve efficiencies of up to 42 percent,” as they harvest a broader range of wavelengths and use the light’s energy more effectively.

In addition to organic semiconductor materials, the e-conversion researchers therefore focus their investigations primarily on the class of materials known as perovskites, which are easy to manufacture from solution and apply as a thin film. The most efficient materials generally contain lead, however, with tin-based perovskites currently seen as an alternative. But the search for variants that contain less hazardous materials continues.

“Ultimately, everything has to pass through the filter of sustainability,” says Hartschuh. This applies, incidentally, to all of the developments in the cluster. The researchers have a whole range of criteria they must weigh up, including sustainability, material and energy inputs, durability, efficiency, availability, suitability for mass use, and costs.

Accelerating the development of new materials

Enlarge

The cluster researchers also want to establish methods that significantly accelerate the development of new materials. “It currently takes 15 years on average for something that works in the laboratory to make it to market,” observes Hartschuh. And so one of the research areas in the cluster is devoted to the issue of time. Its remit is to identify possibilities in operations like high-throughput screenings for running a whole set of experiments on the synthesis and characterization of suitable materials in parallel with slight variations, and for creating agile workflows with the aid of machine learning for the design of materials and optimization of reaction environments – all with the goal of accelerating research and development. In the end, the plan is to create not only a data and support infrastructure, which will enable innovations such as automated labs and virtual working with digital twins, but also a new generation of “data-informed researchers” who have learned to work creatively with such methods.

The researchers are also searching for other ways of storing light energy – in the form of fuels that are transportable. Hydrogen is one example. When it burns, the only ‘waste product’ is water. It would be a clean affair, then, if the production of hydrogen by conventional means did not require a lot of energy, which generally still comes from fossil fuels. In view of this, it would be an elegant solution to directly use the energy from sunlight in photocatalytic techniques – especially if this were possible without the interim steps of electricity generation and subsequent electrolysis, whereby water is split into hydrogen and oxygen.

e-conversion also investigates so-called plasmonic techniques, which involve specially designed nano-surfaces with gold particles that are particularly effective at capturing light as with a superlens. If these antennae are additionally equipped with platinum particles, they stimulate processes such as the conversion of formic acid into hydrogen when exposed to light. With certain material constellations, this photocatalysis is comparatively efficient on a laboratory scale. Similar experiments are running to stimulate other chemical reactions that consume energy, mostly from fossil sources, in conventional techniques.

In one material: absorbing light and storing energy

Developing such hybrid energy concepts is the task given to another research area of the cluster. One approach is the “solar battery,” which absorbs sunlight and stores its energy in one and the same material. In the first instance, the efficiency is not at all that impressive, but the use of other so-called optoionic materials could significantly improve it – initially on a laboratory scale. At the same time, researchers from TUM and the Max Planck Institute for Solid State Research are pursuing the goal of further advancing the technology in the newly founded SolBat Center.

The scientists involved in e-conversion have undertaken not only to contribute directly to technological progress, but also to train a new generation of researchers – more than 150 in fact. In addition, they are planning to develop a new master’s degree course in energy research. Some two-thirds of the total funding will be devoted to fostering new talent. There are also plans for wide-ranging scientific communication designed to address and engage the general public and policymakers. This is a contribution by the researchers to increase acceptance for the energy transition in society and prevent disinformation.