Photovoltaics: Molecular fine-tuning increases the efficiency of tandem solar cells
LMU researchers achieve 31.4 percent efficiency in perovskite-silicon tandem cells with targeted molecular design
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perovskite silicon tandem solar cells are considered a key technology for photovoltaics. Their structure allows sunlight to be used more efficiently than with conventional silicon cells: While the upper perovskite layer absorbs the high-energy blue portion of the light, the underlying silicon layer captures the red range. The interaction of the two materials enables a significantly higher light yield.
An international research team led by Dr. Erkan Aydin, research group leader at LMU, has now significantly developed this approach further. In the scientific journal Joule, the researchers report on the first perovskite-silicon tandem cell that was manufactured entirely in the Munich region. Cooperation partners are the Southern University of Science and Technology (SUSTech) in Shenzhen, China, the City University of Hong Kong and the King Abdullah University of Science and Technology (KAUST) in Saudi Arabia.
A new approach to molecular design
The central element of the tandem cells is the self-assembled monolayer (SAM). This molecular layer, which is only a few nanometers thick, ensures that electrical charges are transported efficiently to the charge collection layers. However, on pyramid-shaped silicon surfaces, conventional SAMs with simple alkyl chains tend to aggregate unevenly. This limits the performance of the cells.
To solve this problem, the researchers developed a special molecule. Its special structure improves charge transport even on rough surfaces and thus creates the basis for a stable interface.
During analyses, the team made a surprising observation: a commercially available SAM precursor contained tiny amounts of bromine-containing impurities. These turned out to be extremely useful, as they neutralize defects at the interface and thus increase the efficiency of the solar cells.
"The fact that such a small chemical change can have such a big effect surprised us," explains project manager Aydin. "This finding shows how crucial the precise interaction of materials at the molecular level is for the energy yield of new types of solar cells."
The researchers combined brominated and non-brominated molecules in order to utilize the positive effects of bromine without compromising chemical stability. Their newly developed SAM structure enables denser molecule packing and better passivation of the interface - which in turn results in higher efficiencies, increased stability and more efficient charge extraction.
31.4 percent efficiency
Through this targeted fine control at the molecular level, the team achieved a cell efficiency of 31.4 percent. This makes the team one of the world's leading laboratories in the development of high-performance perovskite silicon tandem cells. It is particularly noteworthy that these values were achieved on industrially relevant crystalline silicon bottom cells. In addition to the increase in efficiency, the cells also showed improved stability over longer periods of time. The denser molecular packing of the new SAMs protects the sensitive interface from damage at the molecular level.
"As a next step, we want to show that our tandem cells not only prove their performance in the laboratory, but also in accelerated aging tests that provide information about their behavior under real environmental conditions," says Aydin. "At the same time, we are investigating how the technology can be adapted for use in space travel - especially for satellites in low Earth orbits." Interest in particularly lightweight, high-performance and radiation-resistant solar cells is growing rapidly in this area in particular.
Note: This article has been translated using a computer system without human intervention. LUMITOS offers these automatic translations to present a wider range of current news. Since this article has been translated with automatic translation, it is possible that it contains errors in vocabulary, syntax or grammar. The original article in German can be found here.
Original publication
Jian Huang, Letian Zhang, Cem Yilmaz, Geping Qu, Ido Zemer, Rik Hooijer, Siyuan Cai, Ali Buyruk, Hao Zhu, Meriem Bouraoui, Achim Hartschuh, Ryota Mishima, Kenji Yamamoto, Caner Deger, Ilhan Yavuz, Alex K.-Y. Jen, Esma Ugur, Stefaan De Wolf, Igal Levine, Zong-Xiang Xu, Erkan Aydin; "Enhanced charge extraction in textured perovskite-silicon tandem solar cells via molecular contact functionalization"; Joule
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