Most efficient solar module in the world: A more practical record

That records are broken is not uncommon in the world of photovoltaics. By integrating new materials and techniques, the limits of today's mass-market silicon PV modules can sometimes be significantly exceeded. However, what achieves the best values in the lab and research facilities has a long way to go before it produces electricity in significant numbers on house roofs, on balconies, or as parking lot canopies. A report from the Freiburg Fraunhofer Institute for Solar Energy Systems (ISE) is now causing a stir. The "most efficient solar module in the world" has now been developed there, according to a statement from the institute this week. But what does that mean?

In 2023, the ISE developed a silicon-gallium tandem solar cell with an efficiency of 36.1 percent – a world record. And 34.2 percent is the one figure that the Freiburg researchers are now pleased about – this new figure is lower than the old one. And the scientists are also pleased about a second module that achieves 31.3 percent. And this already contains a main difference: it is not individual cells, but modules that are achieving record values in their classes here.

The two new tandem modules are intended to address different application scenarios – and not just in the lab. In both cases, these are III-V modules, meaning that the disadvantages of conventional solar cells are compensated for by a multi-layer structure and materials from main groups III and V. This generates electricity from the different wavelengths in the band gap of the respective upper material. Research has been conducted on such cells at Fraunhofer ISE for 40 years, and thresholds to higher efficiency levels are repeatedly being crossed. However, whether the records will be accepted by the market depends on manufacturing technology and scaling.

Because they are more expensive than normal solar cells, the application of tandem cells has so far been primarily used where efficient energy yield was more important than costs for a long time: in space, for example, with satellite solar cells. Gallium and germanium usually play a role here – expensive materials, especially compared to silicon, which is mostly used today. However, tandem cells are also possible with these, and they still offer efficiency reserves. "III-V in tandem with silicon as a cheaper variant, III-V on germanium as a slightly more efficient variant, are both interesting technological routes for integrated PV applications wherever space is limited," says Andreas Bett, who heads the Freiburg institute.

Research results are actually intended for application

Together with industrial companies from Europe, the researchers involved were able to develop their new modules with funding from the Federal Ministry of Education and Research. What is already established outside of Earth can now, with some adjustments, also generate electricity closer to the Earth's surface. "In the case of the III-V germanium module from the 'Vorfahrt' project, the record cells are already large-format and the processes used for module production are close to series production," says Laura Stevens about the status of her project. This module, which achieves an efficiency of 34.2 percent, has had its glass surface structure optimized again using nanoimprinting.

ISE itself uses equipment that is very similar to that used in industry, which can simplify the transfer. Module materials and processes are industry-standard, i.e., what is already used for space solar cells. The actual costs for integrating the modules would therefore hardly differ from those of previous modules. And something else plays a role, explains Stevens: The module with structured glass and the solar cells contained within it was developed and manufactured in Germany.

The future for the silicon variant is still more open. "III-V on silicon bridges the gap between the state of the art and high-tech products from space research," explains Jonas De Rose, but the combination of the two technologies is not trivial. The success of the Freiburg scientists now lies in the small-scale production of this cell – 218 square centimeters in size, 31.3 percent efficiency, the next important step for the technology from 2023, which set records of 36.1 percent in its class back then.

"For industrial implementation, processes at the interface of the two semiconductors would need to be scaled up further," says the ISE researcher. The necessary knowledge for this is fundamentally available in Germany. "However, this scaling can only be expected if there is corresponding demand from the market," says De Rose. There are interested parties, however. And in both directions: on the one hand, the terrestrial demand for more efficient solar modules is high. Because the space requirements for photovoltaics should not be underestimated in sum – new technological possibilities such as those now further developed by ISE or concentrated PV, which bundles light via additional lenses, could offer advantages here that justify the additional costs.

A little bit of space is necessary

Above all, there is an increasing demand for more cost-effective, yet highly efficient and robust modules for space travel. With the boom in smaller satellites, manufacturers are focused on scaling up for the mass market. Among others, the former Telefunken subsidiary Azur Space, now part of the Canadian 5N Plus group, which has been producing solar cells for extraterrestrial applications since the first German satellite, was involved in the research project for the germanium modules.

The actual progress of the ISE researchers this time lies not primarily in achieving high efficiency with their III-V tandem modules – but in having also taken a significant step towards manufacturing with them. However, whether and when these modules will actually become mass-available is still not reliably foreseeable. And whether they will then be manufactured in Germany or Europe, even less so.

(dmk)