LMU researchers develop molecular ‘anchored net’ against thermal fatigue.
The Aydin Group at LMU Munich has unveiled a novel strategy for making perovskite solar cells more robust against extreme temperature fluctuations. To this end, the researchers led by Dr. Erkan Aydin, group leader at LMU’s Department of Chemistry and Pharmacy, combined two molecular approaches. Their goal was to stabilize both the grain structure within the perovskite material and the interfaces of the solar cells, with a particular focus on enhancing the interaction between the perovskite layer and the underlying substrate. This enables the solar cells to maintain stable performance under the extreme thermal cycling typical of Low Earth Orbit (LEO), as well as in other harsh environmental conditions. Their results have been published in the journal Nature Communications.
A promising but sensitive technology
Regarding the background: Perovskite solar cells are considered one of the most promising next-generation photovoltaic technologies. They are relatively inexpensive to manufacture and achieve high efficiencies.
However, their mechanical stability is an issue. In particular, when confronted with strong temperature fluctuations in LEO – for example, in the range between −80 and +80 degrees Celsius – materials inside the solar cell can expand and contract to varying extents. This creates mechanical stresses, which lead to cracks, delamination, or drops in performance.
Such conditions do not only arise in the laboratory during accelerated aging tests, but also in certain operational environments, such as low Earth orbit, where the solar cells on satellites are repeatedly exposed to direct sunlight and then cold within short periods of time. As a result, based on the spacecraft design and the orbit, these temperature extremes may vary, and the team selected a representative temperature range for this.
Molecular ‘anchored net’ for solar cells
Aydin’s team developed a two-step molecular reinforcement strategy to specifically stabilize particularly vulnerable regions of the solar cell.
Firstly, the researchers incorporated α-lipoic acid into the perovskite layer. During the fabrication process, these molecules partially polymerize and form a sort of network at the grain boundaries of the material. This reduces defects and increases mechanical stability.
Secondly, the scientists reinforced the interface between the electrode material and the perovskite layer with specially developed molecules. Particularly successful was a molecule with a sulfonium group, which forms a very strong chemical bond at the interface – namely, DMSLA (dimethylsulfonium-lipoic acid).
“We can think of these molecules as a flexible, anchored net,” explains Aydin. “They keep the perovskite light-absorbing layer integrated with the substrate, allowing it to adapt to temperature changes while preventing delamination.”
Efficiencies of over 25 percent
The optimized solar cells achieve efficiencies of 26 percent, which is around 3 percent higher than the control unit used in the work. In experiments, this performance was largely sustained even after repeated extreme temperature cycles. After 16 cycles between -80 and +80 degrees Celsius, the modified solar cells retained 84 percent of their original efficiency, while the performance of reference cells fell to a much greater extent.
The experiments also show that it is not just the number of temperature shifts that matters, but above all the overall duration of the thermal strain. Most material degradation occurred during the initial cycles.
Prospective applications for space travel and flexible photovoltaics
According to the researchers, the findings provide important insights for the further development of durable perovskite solar cells. “Our work shows it’s possible to improve the mechanical stability of perovskite solar cells in a targeted manner when you address the critical interfaces and grain boundaries in the material,” says Aydin. “This brings us one step closer to the practical use of this technology,” and he adds, “As a research group based in Munich, we are developing strategies to prepare perovskite-based solar cells for space applications. Further work will follow to gain a deeper understanding of how our cells behave under such extreme conditions.”
The technology is particularly interesting for applications with extreme temperature conditions, such as space flight, airborne platforms in the stratosphere, or the lightweight solar modules of the future.