Tandem solar cells with perovskite: nanostructures help in many ways
Scanning electron microscopy of perovskite silicon tandem cells in cross-section with nanotexture and back-reflector layer (golden). © P. Tockhorn/HZB
By the end of 2021, teams at HZB had presented perovskite silicon tandem solar cells with an efficiency close to 30 percent. This value was a world record for eight months, a long time for this hotly contested field of research. In the renowned journal Nature Nanotechnology, the scientists describe how they achieved this record value with nanooptical structuring and reflective coatings.
Tandem solar cells made of perovskite and silicon enable significantly higher efficiencies than silicon solar cells alone. Tandem cells from HZB have already achieved several world records. Most recently, in November 2021, HZB research teams achieved a certified efficiency of 29.8 % with a tandem cell made of perovskite and silicon. This was an absolute world record that stood unbeaten at the top for eight months. It was not until the summer of 2022 that a Swiss team at EPFL succeeded in surpassing this value.
Joined forces
Three HZB teams had worked closely together for the record-breaking tandem cell. Now they present the details in Nature Nanotechnology. The journal also invited them to write a research briefing, in which they summarise their work and give an outlook on future developments.
Textures improves the performance
"Our competences complement each other very well," says Prof. Dr. Christiane Becker, who developed the world record cell with the team led by Dr. Bernd Stannowski (silicon bottom cell) and Prof. Dr. Steve Albrecht (perovskite top cell). Becker's team introduced a nanooptical structure into the tandem cell: a gently corrugated nanotexture on the silicon surface. "Most surprising, this texture brings several advantages at once: it reduces reflection losses and ensures a more regular perovskite film formation," says Becker. In addition, a dielectric buffer layer on the back of the silicon reduces parasitic absorption at near-infrared wavelengths.
As a conclusion, the researchers hold: customised nanotextures can help to improve perowskite semiconductor materials on diverse levels. These results are not only valuable for tandem solar cells made of perovskite and silicon, but also for perovskite-based light-emitting diodes.
- Langbeinites show talents as 3D quantum spin liquidsA 3D quantum spin liquid has been discovered in the vicinity of a member of the langbeinite family. The material's specific crystalline structure and the resulting magnetic interactions induce an unusual behaviour that can be traced back to an island of liquidity. An international team has made this discovery with experiments at the ISIS neutron source and theoretical modelling on a nickel-langbeinite sample.
- Green hydrogen: ‘Artificial leaf’ becomes better under pressureHydrogen can be produced via the electrolytic splitting of water. One option here is the use of photoelectrodes that convert sunlight into voltage for electrolysis in so called photoelectrochemical cells (PEC cells). A research team at HZB has now shown that the efficiency of PEC cells can be significantly increased under pressure.
- Green hydrogen from direct seawater electrolysis- experts warn against hypeAt first glance, the plan sounds compelling: invent and develop future electrolysers capable of producing hydrogen directly from unpurified seawater. But a closer look reveals that such direct seawater electrolysers would require years of high-end research. And what is more: DSE electrolyzers are not even necessary - a simple desalination process is sufficient to prepare seawater for conventional electrolyzers. In a commentary in Joule, international experts compare the costs and benefits of the different approaches and come to a clear recommendation.