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Novel solar cell deposition from liquid silicon

Research at IEK-5 paves the way to the next generation of thin film silicon electronics

Jülich, 15. August 2014 - Scientists at IEK-5 Photovoltaik, in cooperation with the company Evonik, have developed a solar cell consisting of a thin film of a liquid silicon compound. With an efficiency of 3.5 percent, this solar cell is about seven times more efficient than previous cells of this type. The scientists are optimistic regarding the prospects of further efficiency increase of these low cost solar cells. In this way, the approach which is considered a promising basis for the next generation of thin-film electronics, would also become economically viable.

FlüssigsilanEin Glas-Substrat mit mehreren Solarzellen aus dem flüssig-prozessierten Silizium im Sonnensimulator, in dem der Wirkungsgrad gemessen wird.
Copyright: Forschungszentrum Jülich

Silicon is the most used world wide and best known semiconductor. However, the processing of silicon is very costly and resource intensive. This is exactly the challenge addressed by the liquid silicon based approach developed by scientists at IEK-5 in collaboration with the strategic research (CREAVIS) at the speciality chemicals company Evonik. "The liquid compound can be inexpensively processed and converted into the well-known semiconductor silicon", explains Juelich scientist Thorsten Bronger, first author of the study. He and his colleagues contributed their experience in the development and optimization of solar cells, while Evonik brought in its competence in innovative materials chemistry.

Instead of relying on the sawing of massive silicon blocks into thin wafers, the approach uses silicon in a liquid chemical compound that is deposited on a glass substrate as a thin film of a few hundred nanometers. After that, the film is converted into a solid layer with semiconducting properties. After the application of contacts, the resulting device can be used as a solar cell, which, however, does not yet reach the efficiency cells from conventional maufacturing: depending on the type of solar cell, these range from 10 to over 20 percent. "For applications that do not demand a high conversion efficiency, our approach could become a cost effective alternative", Bronger remarks. Possible applications besides solar cells include also displays, Radio Frequency Identification (RFID), biological sensors and medical equipment.

The fabrication of thin semiconductor films from solution itself is not new. In the production of organic solar cells, which consist of carbohydtrate compounds, this is a long established procedure. "When we started in 2009, the approach was considered extremely challengig. At that time, there were only a few research groups world wide that investigated this material", Bronger remembers. At the beginning, the scientists faced the problem of homogeneous film formation from the liquid silicon: in some occasions, the film ruptured or holes formed. "It is comparable to the spreading of honey with a spoon: the surface tension leads to the formation of small gaps", the physicist explains. Gaps in the silicon film, however, ruin the solar cell, since they lead to shunt formation.

After approximately two years of research, the scientists had developed the first working solar cell. Two more years later, the strongly improved material quality for the first time enabled an efficiency of 3.5 percent. "This achievement exceeds the previous results of other research teams by a factor of seven. It demonstrates that solution-processed silicon has a much higher potential than previously assumed", Bronger comments on the result published in the journal "Advanced Energz Materials". He estimates that the efficiency will have to be increased by at least another 2.5 percents before industrial application becomes economically viable. To this end, further investigation is required.

Original publication:

"Solution-based Silicon in Thin-Film Solar Cells",
Torsten Bronger et al., Advanced Energy Materials, Volume 4, Issue 11, first published online: 27. März 2014, DOI: 10.1002/aenm.201301871

Further Informationen:

Institute of Energy and Climate Research 5 – Photovoltaics (IEK-5)


Dr. Torsten Bronger
Institut für Energie- und Klimaforschung – Photovoltaik (IEK-5)
Forschungszentrum Jülich
Telefon: 02461 61-2954