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Investigating new semiconductors for solar cells

Crystalline silicon is used as the semiconductor in many solar cells but it is expensive. Layered semiconductors such as indium selenide (InSe) and gallium selenide (GaSe) of the chalcogenide chemical family are promising candidates for solar cells as they show ideal surface and interface properties and can also reduce the costs 10-fold. To date, however, there have been problems making thin films of these layered chalcogenides and they have exhibited unfavourable properties. This has prohibited the use of these materials in solar cells.

To feasibly use the semiconductors in solar cells, the film of material must be highly textured and photoactive. The new thin films were characterised by their optoelectronic properties which must be optimised with respect to solar conversion efficiency. Films of layered compounds can be prepared on different layered substances such as graphite and other chalcogenides. The films are epitaxial which means that the thin layer has the same crystalline orientation as the substrate onto which it is deposited. The process the researchers used is called van der Waals epitaxy. Doping the semiconductor with impurities can also improve the properties of the film. The 3 partners worked on developing semiconductors primarily in single crystal form and then in epitaxial films. The techniques used to characterise the materials included photoelectron spectroscopy.

Both InSe and GaSe single crystals were prepared in high doping concentrations and they were well characterised. Thin films of both materials could be deposited by van der Waals epitaxy and the resulting films were fully characterised with respect to their optoelectronic properties. The InSe film was shown to have suitable properties for PV applications. It was not possible, however, to prepare doped films by van der Waals epitaxy. Other materials were also studied and these showed promising PV properties. These include GaSe/InSe/indium oxide materials which show photocurrents close to the maximum and conversion efficiencies of up to 11% in single crystals.

Reported by

Technische Universität Darmstadt
Petersenstrasse 23
64287 Darmstadt
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