Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Hope for silicon solar cells with significantly improved efficiency: New synthesis route to soluble silicon clusters

15.11.2019

Theoretical calculations indicate that under certain conditions silicon can endow solar cells with a much higher efficiency. Small silicon clusters may provide a source of accordingly modified silicon. However, to date these clusters have not been accessible in soluble form, a prerequisite for flexible processing. Researchers at the Technical University of Munich (TUM) have now discovered a simple synthesis approach.

Today, the best silicon solar cells in the world have an efficiency of 24 percent. The theoretical limit is around 29 percent. "This is because silicon normally crystallizes in a diamond structure which provides only an indirect band gap," explains Thomas Fässler, Professor of Inorganic Chemistry with Focus on New Materials at the Technical University of Munich.


PhD student Kevin Frankiewicz works with nine-atom silicon clusters dissolved in liquid ammonia in the laboratory of Prof. Fässler, Professorship of Inorganic Chemistry with Focus on New Materials.

Uli Benz / TUM


Nine-atom silicon clusters could be precursors of larger structures. Theoreticians hope to obtain materials that have a direct band gap and thus enable significantly more efficient solar cells.

A. J. Karttunen / Aalto University

Researchers thus dream of materials in which silicon atoms are arranged in a manner that creates a direct band gap that they can exploit for solar energy production. The scientists view these small silicon clusters as model compounds for this purpose because the atoms can be arranged differently than in crystalline silicon.

"These kinds of compounds are also interesting for a variety of other chemical experiments," says Professor Fässler. “Using only a few synthesis steps we can now join four and nine silicon atoms into tetrahedrons or near-spherical structures. However, in the past, the synthesis and isolation of the atomic clusters was very laborious. Now, we have taken a significant step forward."

A cluster of nine silicon atoms

Fusing potassium and silicon results in a compound with 12 potassium and 17 silicon atoms, a gray powder. First author Lorenz Schiegerl managed to stabilize the soluble, nine-atom clusters in liquid ammonia using a clever trick: He added an organic molecule to the ammonia that encapsulates the potassium atoms.

"This simple synthesis, starting from elemental silicon, opens the door to myriad chemical experiments with these clusters," says Professor Fässler. "In the solvent pyridine, for example, the cluster is stabilized by two hydrogen atoms, similar to the presumed intermediates in large-scale production of polycrystalline silicon, which is prepared using silanes or chlorosilanes for commercially available solar cell modules."

Creating new structures

Particularly promising is another reaction path to obtaining compounds made of silicon clusters. Here, three of the nine silicon atoms combine with molecules that in turn contain silicon or, for example, carbon or tin. Clusters with the highest currently known silicon concentrations are found in these reddish-brown solutions. This opens up novel possibilities for depositing silicon with modified structures out of solution.

"Extending this line of thinking, it should also be possible to build larger silicon structures using clusters of clusters. That would nearly close the gap to the aspirations of theoreticians," says Prof. Fässler. "In any case, we have opened the door to fascinating, new chemistry."

The project was funded by WACKER Chemie AG as part of the "WACKER Institute for Silicon Chemistry" at TUM, the Bavarian research association "Solar Technologies Go Hybrid" and the Academy of Finland. The electron structure calculations were done by the team of Prof. Karttunen, Aalto University, Helsinki (Finland) at the Finnish IT Center for Science (CSC).

Wissenschaftliche Ansprechpartner:

Prof. Dr. Thomas F. Fässler
Technical University of Munich
Professorship for Inorganic Chemistry with Focus on New Materials
Lichtenbergstr. 4, 85748 Garching, Germany
Tel.: +49 89 289 13131
E-Mail: thomas.faessler@lrz.tum.de

Originalpublikation:

Silicon Clusters with Six and Seven Unsubstituted Vertices via a Two-step Reaction from Elemental Silicon
L. J. Schiegerl, A. J. Karttunen, W. Klein, T. F. Fässler
Chemical Science, 2019, 10, 9130 – 9139 – DOI: 10.1039/C9SC03324F
https://pubs.rsc.org/en/content/articlelanding/2019/sc/c9sc03324f

Charged Si9 Clusters in Neat Solids and the Detection of [H2Si9]2− in Solution – A Combined NMR, Raman, Mass Spectrometric, and Quantum Chemical Investigation
L. J. Schiegerl, A. J. Karttunen, J. Tillmann, S. Geier, G. Raudaschl-Sieber, M. Waibel, T. F. Fässler
Angew. Chem. Int. Ed. 2018, 57, 12950 –12955 – DOI: 10.1002/anie.201804756
https://onlinelibrary.wiley.com/doi/10.1002/ange.201804756

Weitere Informationen:

https://www.department.ch.tum.de/en/acnm/welcome/ Homepage of Prof. Fässler's group
https://www.tum.de/nc/en/about-tum/news/press-releases/details/35779/ Press release on the website of TUM with additional links

Dr. Ulrich Marsch | Technische Universität München

More articles from Power and Electrical Engineering:

nachricht Fraunhofer starts development of refrigerant-free, energy-efficient electrocaloric heat pumps
09.12.2019 | Fraunhofer IPM

nachricht A solution for cleaning up PFAS, one of the world's most intractable pollutants
06.12.2019 | Colorado State University

All articles from Power and Electrical Engineering >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: How to induce magnetism in graphene

Graphene, a two-dimensional structure made of carbon, is a material with excellent mechanical, electronic and optical properties. However, it did not seem suitable for magnetic applications. Together with international partners, Empa researchers have now succeeded in synthesizing a unique nanographene predicted in the 1970s, which conclusively demonstrates that carbon in very specific forms has magnetic properties that could permit future spintronic applications. The results have just been published in the renowned journal Nature Nanotechnology.

Depending on the shape and orientation of their edges, graphene nanostructures (also known as nanographenes) can have very different properties – for example,...

Im Focus: Electronic map reveals 'rules of the road' in superconductor

Band structure map exposes iron selenide's enigmatic electronic signature

Using a clever technique that causes unruly crystals of iron selenide to snap into alignment, Rice University physicists have drawn a detailed map that reveals...

Im Focus: Developing a digital twin

University of Texas and MIT researchers create virtual UAVs that can predict vehicle health, enable autonomous decision-making

In the not too distant future, we can expect to see our skies filled with unmanned aerial vehicles (UAVs) delivering packages, maybe even people, from location...

Im Focus: The coldest reaction

With ultracold chemistry, researchers get a first look at exactly what happens during a chemical reaction

The coldest chemical reaction in the known universe took place in what appears to be a chaotic mess of lasers. The appearance deceives: Deep within that...

Im Focus: How do scars form? Fascia function as a repository of mobile scar tissue

Abnormal scarring is a serious threat resulting in non-healing chronic wounds or fibrosis. Scars form when fibroblasts, a type of cell of connective tissue, reach wounded skin and deposit plugs of extracellular matrix. Until today, the question about the exact anatomical origin of these fibroblasts has not been answered. In order to find potential ways of influencing the scarring process, the team of Dr. Yuval Rinkevich, Group Leader for Regenerative Biology at the Institute of Lung Biology and Disease at Helmholtz Zentrum München, aimed to finally find an answer. As it was already known that all scars derive from a fibroblast lineage expressing the Engrailed-1 gene - a lineage not only present in skin, but also in fascia - the researchers intentionally tried to understand whether or not fascia might be the origin of fibroblasts.

Fibroblasts kit - ready to heal wounds

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

The Future of Work

03.12.2019 | Event News

First International Conference on Agrophotovoltaics in August 2020

15.11.2019 | Event News

Laser Symposium on Electromobility in Aachen: trends for the mobility revolution

15.11.2019 | Event News

 
Latest News

City research draws on Formula 1 technology for the construction of skyscrapers

10.12.2019 | Architecture and Construction

Reorganizing a computer chip: Transistors can now both process and store information

10.12.2019 | Information Technology

Could dark carbon be hiding the true scale of ocean 'dead zones'?

10.12.2019 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>