Scientists Meet Scientists – Virtual Wednesday Coffee Talk by Prof. Dr. Thomas Fässler on entitled “New Synthesis Approach for Soluble Silicon Clusters – Anticipating Silicon Solar Cells with Significantly Improved Efficiency”

On January 27th, Prof. Dr. Thomas Fässler (TUM Department of Chemistry) will give a talk entitled “New Synthesis Approach for Soluble Silicon Clusters – Anticipating Silicon Solar Cells with Significantly Improved Efficiency”. 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 on soluble form, a prerequisite for flexible processing. Professor Fässler and his team have now discovered a simple synthesis approach. Today, the best silicon solar cells in the world have an efficiency of 24 percent with the theoretical limit being around 29 percent. This is because silicon normally crystalizes in a diamond structure, which provides only an indirect band gap. Researches 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. Using only a few synthesis steps, Professor Fässler and his team can now join four and nine silicon atoms into tetrahedrons or near-spherical structures. Fusing potassium and silicon results in a compound with 12 potassium and 17 silicon atoms. By adding organic molecule to the ammonia, which encapsulates the potassium atoms, it has been achieved to stabilize the soluble, nine-atom clusters in liquid ammonia.

According to Professor Fässler, this simple synthesis, starting from elemental silicon, opens the door to myriad chemical experiments with these cluster. In the future, it should also be possible to build larger silicon structures using clusters of clusters, which would nearly close the gap to the aspirations of theoreticians (TUM press release).


Schiegerl, L. J., Karttunen, A. J., Klein, W., Fässler, T. F., „Silicon Clusters with Six and Seven Unsubstituted Vertices via a Two-Step Reaction from Elemental Silicon“, Chemical Science, 2019/10. DOI: 10.1039/C9SC03324F.


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