"Sandwiched" graphene holds promise for thin-film solar cells
Scientists at the Helmholtz Zentrum Berlin (HZB) have found that graphene retains its remarkable electrical conductive properties even when it is in close contact with materials like glass and silicon. It could be a key discovery for the development of better thin-film solar cells.
Graphene, a one-atom thick sheet of carbon atoms, is often touted as a wonder material: it's strong, versatile, and has excellent electric properties that have made it one of the prime candidates for building the next generation of transistors. Crucially for photovoltaics applications, it is also transparent, meaning it can let photons inside a solar cell without obstructing them.
However, graphene is extremely thin, and since materials in electronics often have to be laid on top of each other with very little wiggle room, scientists have long suspected that close contact of a single graphene sheet with the adjacent layers of a solar cell could severely degrade its performance and render it useless in a practical setting.
Dr. Marc Gluba and Prof. Norbert Nickel at HZB set out to quantify the loss in performance that occurred when a single graphene sheet was sandwiched between the layers of a typical thin-film solar cell. To do so, they laid a single graphene sheet on top of a glass substrate and then coated the sheet with a thin layer of silicon.
The result was rather surprising: the electrical properties of the sheet changed very little, and the material could still be detected and didn't lose structural integrity despite being only about 0.03 nanometers thick.
The embedded graphene showed carrier mobility about 30 times higher than zinc-oxide, a common material in the industry. This is crucial, because in semiconductors a higher carrier mobility is associated with better device performance. New designs for thin-film solar cells could one day greatly benefit from this performance boost.
Gluba and Nickel are now facing the challenge of connecting the thin graphene contact layer, which is only one atom thick, to external contacts for further testing.
A paper detailing the finding appears in the journal Applied Physics Letters.