Major leap towards graphene for solar cells

Graphene was deposited onto a glass substrate. The ultrathin layer is but one atomic layer thick (0.3 Angström, or 0.03 nanometers), although charge carriers are able to move about freely within this layer. This property is retained even if the graphene layer is covered with amorphous or polycrystalline silicon.

Graphene was deposited onto a glass substrate. The ultrathin layer is but one atomic layer thick (0.3 Angström, or 0.03 nanometers), although charge carriers are able to move about freely within this layer. This property is retained even if the graphene layer is covered with amorphous or polycrystalline silicon. © Marc A. Gluba/HZB

Surprising result: Graphen retains its properties even when coated with silicon

Graphene has extreme conductivity and is completely transparent while being inexpensive and nontoxic. This makes it a perfect candidate material for transparent contact layers for use in solar cells to conduct electricity without reducing the amount of incoming light  - at least in theory. Whether or not this holds true in a real worldsetting is questionable as there is no such thing as "ideal" graphene - a free floating, flat honeycomb structure consisting of a single layer of carbon atoms: interactions with adjacent layers can change graphene's properties dramatically. Now, Dr. Marc Gluba and Prof. Dr. Norbert Nickel of the HZB Institute for Silicon Photovoltaics have shown that graphene retains its impressive set of properties when it is coated with a thin siliconfilm. These findings have paved the way for entirely new possibilities to use in thin-film photovoltaics.

"We examined how graphene's conductive properties change if it is incorporated into a stack of layers similar to a silicon based thin film solar cell and were surprised to find that these properties actually change very little," Marc Gluba explains.

To this end, they grew graphene on a thin copper sheet, next transferred it to a glass substrate, and finally coated it with a thin film of silicon. They examined two different versions that are commonly used in conventional silicon thin-film technologies: one sample contained an amorphous silicon layer, in which the silicon atoms are in a disordered state similar to a hardened molten glas; the other sample contained poly-crystalline silicon to help them observe the effects of a standard crystallization process on graphene's properties.

Even though the morphology of the top layer changed completely as a result of being heated to a temperature of several hundred degrees C, the graphene is still detectable.

"That's something we didn't expect to find, but our results demonstrate that graphene remains graphene even if it is coated with silicon," says Norbert Nickel. Their measurements of carrier mobility using the Hall-effect showed that the mobility of charge carriers within the embedded graphene layer is roughly 30 times greater than that of conventional zinc oxide based contact layers. Says Gluba: "Admittedly, it's been a real challenge connecting this thin contact layer, which is but one atomic layer thick, to external contacts. We're still having to work on that." Adds Nickel: "Our thin film technology colleagues are already pricking up their ears and wanting to incorporate it."

The researchers obtained their measurements on one square centimeter samples, although in practice it is feasible to coat much larger areas than that with graphene.

This work was recently published in Applied Physics Letters Vol. 103, 073102 (2013).
Authors: M. A. Gluba, D. Amkreutz, G. V. Troppenz, J. Rappich, and N. H. Nickel

doi: 10.1063/1.4818461

arö


You might also be interested in

  • Quantsol Summer School 2024 - Call for Application
    News
    17.04.2024
    Quantsol Summer School 2024 - Call for Application
    Registration for Quantsol is now open!

    The International Summer School on Photovoltaics and New Concepts of Quantum Solar Energy Conversion (Quantsol) will be held in September 1-8, 2024 in Hirschegg, Kleinwalsertal, Austria. The school is organised by the Helmholtz-Zentrum Berlin and the Technical University of Ilmenau. Applications can be submitted through the school’s homepage until Friday 31st of May 2024, 23.59h CET.

  • A simpler way to inorganic perovskite solar cells
    Science Highlight
    17.04.2024
    A simpler way to inorganic perovskite solar cells
    Inorganic perovskite solar cells made of CsPbI3 are stable over the long term and achieve good efficiencies. A team led by Prof. Antonio Abate has now analysed surfaces and interfaces of CsPbI3 films, produced under different conditions, at BESSY II. The results show that annealing in ambient air does not have an adverse effect on the optoelectronic properties of the semiconductor film, but actually results in fewer defects. This could further simplify the mass production of inorganic perovskite solar cells.
  • Vortrag "BIPV - zwischen Bauwelt und Photovoltaik"
    Nachricht
    15.04.2024
    Vortrag "BIPV - zwischen Bauwelt und Photovoltaik"
    Im Rahmen der The smarter-e Europe/Intersolar Europe 2024 findet eine Vortragssession organisiert von der Allianz BIPV und dem Solarenergieförderverein Bayern e.V. zum Thema "Bauwerkintegrierte Photovoltaik (BIPV)" statt.

    Datum: 19. Juni 2024, 16:00 -17:45 Uhr
    Ort:       Messe München, Halle A3, Stand A3.150