Growing graphene on silver could improve solar cells

Graphene is an amazing material, but it has its flaws. Electricity can run through it at super-fast speeds, but graphene in its natural form can’t start and stop its flow, limiting its use for applications like solar cells.

One potential fix is to pair it with other materials, creating a hybrid that borrows needed characteristics from both ingredients.

A Northwestern University graduate student recently discovered a way to combine graphene with silver, which has interesting optical properties and is already widely used in solar cells. Pairing the two up until now eluded scientists because silver is not compatible with the most common technique for making graphene.

Though there are other existing and emerging approaches, graphene is generally made in an oven stocked with gases like methane and propane. At high temperatures, graphene naturally pulls out of the gases and deposits itself in sheets on copper placed in the oven. But when you replace the copper with silver, it doesn’t work.

“The methane won’t break down, it’ll just hit the hot silver and bounce off and remain methane, so there’s no carbon source to actually grow the graphene,” Argonne National Laboratory staff scientist Nathan Guisinger said in a release.

The secret was to make sure the silver was highly pure and flat. Researchers from Northwestern and Argonne covered the silver in ions that ate away impurities, then ensured its surface was totally flat. They kept the silver in a high-vacuum environment, which limited its exposure to air and water.

It worked: Graphene deposited onto the silver.

By using the new technique, the team was also able to grow graphene at around 1400 degrees Fahrenheit, down from the more usual 1800+ degrees. Working at a lower temperature slows down the growth process, which could allow for more control over the graphene.

The researchers think their work could have applications in light detectors and light absorbing devices like solar cells. They are also interested in pairing graphene with other atom-thick materials.