Graphene Works and Plays Well With Other Materials

Dean Sigler Electric Powerplants, Sustainable Aviation 0 Comments

Graphene is a highly promising material, one atom thick, strong enough to support an elephant standing on a pencil (only theoretically so far, with no actual demonstration having taken place), and electrically conductive.  All these properties bode well for its use in batteries, solar cells, and even energy-storing structural members.  One concern, however, has been in how graphene would interact with other materials in a practical setting.  After all, so far most experiments with graphene have taken place at the atomic level, not a feasible working arrangement for the ham-handed and those without scanning electron microscopes in their garage workshops.

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0.03 nanometer thick graphene was deposited onto a glass substrate, then covered with amorphous or polycrytsalline silicon, but retained its electrical properties.  Illustration Marc A. Gluba/HZB

Dr. Marc Gluba and Professor Dr. Norbert Nickel of the Helmholz Zentrum Berlin have, doubtless with some pretty intense tools available at their Institute for Silicon Photovoltaics, managed to coat a graphene film with a thin silicon film.

According to the Institute, “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 glass; the other sample contained poly-crystalline silicon to help them observe the effects of a standard crystallization process on graphene’s properties.”

The scientists were “surprised” by the outcome.  Dr. Gluba explains, “”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.”

Professor Dr. Nickel adds, “That’s something we didn’t expect to find, but our results demonstrate that graphene remains graphene even if it is coated with silicon.”

Taking measurements of charge carrier mobility within the embedded graphene layer, they found that mobility to be “30 times greater than that of conventional zinc oxide based contact layers.”  Gluba admits, “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.”   Nickel says, “Our thin film technology colleagues are already pricking up their ears and wanting to incorporate it.”

This work was recently published in Applied Physics Letters Vol. 103, 073102 (2013), in which some drawbacks are made manifest in the paper’s abstract.

“However, the crystallinity of the silicon cap has large influence on the field-induced doping of graphene. Temperature dependent Hall-effect measurements reveal that the mobility of embedded graphene is limited by charged-impurity and phonon-assisted scattering.”  In other words, as all good science papers end, further research is required.

Even though the researchers worked with one square centimeter samples, it is “feasible” to coat larger areas with graphene. The resulting solar cells using this technology would doubtless be the thinnest, lightest, and perhaps most powerful possible.

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