New Materials for Photovoltaics
The use of solar energy is one of the most important technologies for a sustainable energy supply. Modern silicon-based solar cells now achieve efficiencies of just under 28 per cent. However, in order to meet the world’s growing energy demand in a climate-friendly manner in the long term, more efficient photovoltaic technologies are required. This is precisely where our research sets in: The aim is to develop novel materials for highly efficient multi-junction solar cells with efficiencies of over 50 per cent.
Conventional solar cells usually consist of just a single active semiconductor junction. As a result, a large proportion of sunlight cannot be utilised optimally, as different wavelengths carry different amounts of energy. Multi-junction solar cells solve this problem by combining several layers with different band gaps. Each sub-cell absorbs a specific range of the solar spectrum particularly efficiently. As a result, approximately 150 per cent more solar energy can be converted into electrical energy.
High-performance cells with multiple junctions, which achieve efficiencies of over 39 per cent, already exist today. However, these are often based on very expensive III-V semiconductors and are mainly used in specialised applications such as space technology. Cost-effective industrial applications have so far been virtually impossible. At the same time, new material systems such as halide perovskites are becoming increasingly important. They enable high efficiencies with very thin layers, but often have limited chemical stability.
Our research therefore focuses on an alternative class of materials based on chalcogenide compounds. These materials are considered to be particularly chemically stable and have great potential for future thin-film solar cells. By specifically combining different chemical elements, their optical and electrical properties can be tailored. Of particular importance here is the bandgap, which determines which parts of the sunlight can be absorbed.
The group first investigates material combinations that have been identified, using quantum theoretical calculations, as stable and suitable for PV applications. The focus is on materials consisting of elements that are as widely available, cost-effective and low-toxicity as possible. Subsequently, thin layers of material are produced in a vacuum and examined using modern analytical techniques. These include, amongst others, electron microscopy, X-ray diffraction, and optical and electrical measurement methods.
A particular focus is on combinatorial materials research. In this approach, the chemical composition of the materials is deliberately varied across the sample surface. This allows many different material combinations to be investigated simultaneously. This method saves time and reduces the experimental workload, whilst enabling the efficient identification of particularly suitable compositions for use in multi-junction solar cells.
In the long term, the findings are to be incorporated into the development of novel thin-film multi-junction solar cells. The aim is to create a new generation of high-performance, cost-effective and durable photovoltaic technologies. This combines fundamental research in materials science with concrete applications for the energy technology of the future.