Photovoltaics

Photovoltaics is perceived to be a game changer for the global energy system by the Global Alliance of Solar Energy Research Institutes (GA-SERI), of which Fraunhofer ISE is a member together with NREL (USA) and AIST (Japan). An article to this effect was published in the journal “Science” in May 2019. Dramatic cost reduction and the rapid expansion of production capacity have led to this perception. Not only the electricity sector but also transport, heat, industry and chemical processing will be powered to a large extent by electricity in future. This scenario offers opportunities but also raises challenges – both at the level of the energy system and also with regard to research and industry. At the end of 2018, PV power amounting to about 488 GW was installed. The dominating cost share of PV power plants, the investment costs, has been decreasing since 2006 by an average of about 13 % per year, in total by 75 %, due to technological progress, scaling and learning effects. In Germany, competitive levellized costs of electricity of 4 to 5 euro cents per kWh can be achieved today. In order to successfully realize the energy transformation and approach the goal of a CO₂-free energy supply, we need to expand photovoltaic installation to an extent that can no longer be accommodated on roofs or open land areas. We have thus initiated work on the topic of “Integrated Photovoltaics” at Fraunhofer ISE.

Research and development have made essential contributions to this success story. Fraunhofer ISE contributes to continuous improvement in efficiency and use of material resources with its excellent R&D results. Central keywords include the contact passivation technology (Tunnel Oxide Passivated Contact – TOPCon) that was developed at Fraunhofer ISE and the development of special high-performance silicon, which forms the basis for new record solar cell efficiencies. We are transferring wafer processing from its previous location in Freiberg to the Center for Silicon Photovoltaics (CSP) located in Halle. A further major topic there is recycling, which is becoming increasingly important. Preparatory research for industrial implementation is carried out by Fraunhofer ISE in our PV-TEC – Photovoltaic Technology Evaluation Center.

A promising approach to overcome the Auger limit of 29.4 % for the efficiency of single-junction silicon solar cells is presented by tandem solar cells. In developing tandem concepts, we benefit from competence gained over more than four decades in silicon solar cells and in the production of multijunction solar cells. In 2019, we were able to improve the world record for a monolithically produced, multi-junction solar cell of III-V semiconductors and silicon to an efficiency value of 34.1 %. We achieved a value of 24.5 % for a tandem cell consisting of perovskite on silicon. In concentrator technology, we demonstrated top efficiencies for multi-junction cells of up to 46.1 % and a record module efficiency of 41.4 %. Our work on organic and perovskite solar cells opens up interesting perspectives and application areas.

In addition, Fraunhofer ISE further develops successful procedures for the accurate characterization and yield analysis of cells and modules. Our accredited calibration laboratory, CalLab PV Modules, achieves an internationally leading measurement uncertainty of only 1.1 %. With our portfolio, we are well equipped for the future and are contributing to developing yet more efficient photovoltaics – with respect to the energy yield, manufacturing procedures, use of materials and a sustainable processing chain.

More than 90 % of all solar cells that are produced throughout the world are made of crystalline silicon. The keys to this dominant market position are a robust and cost-effective manufacturing process on the one hand and the high efficiency and great reliability of silicon-based PV modules on the other. In particular, efficiencies play a decisive role for further reducing the levellized cost of electricity and is thus the focus of research activities.

Fraunhofer ISE supports the research and development by manufacturers of materials, modules and production equipment with its internationally unique R&D infrastructure in laboratories and prototype production facilities covering more than 3000 m² floor area. The scientific and technological competence of our more than 300 scientists, engineers and technicians spans silicon material, through solar cells and modules, to complete systems.

As a result, our cooperation partners have access not only to individual technologies but can work together with us along the complete value chain. The technological readiness level encompasses the complete bandwidth from laboratory research to industrially relevant development. With new technologies and international records in efficiencies from our research laboratories, we repeatedly establish new scientific trends in photovoltaics and thus provide important stimuli for new developments. In our technological centers with their industrially relevant infrastructure, PV-TEC and SiM-TEC, we can evaluate more mature concepts under realistic conditions and develop innovative manufacturing processes that are ready for transfer to industry. In addition to modern technology, thorough characterization of the underlying processes and careful quality assurance throughout the entire value chain are extremely valuable for our clients and cooperation partners. As a new beacon for our solar cell research, we will be opening the new building for our Center for High Efficiency Solar Cells in 2020.