Graphene sees the light: Sheets of carbon just one atom thick could be used in photovoltaic cells

Graphene sees the light: Sheets of carbon just one atom thick could be used in photovoltaic cells

Graphene, a one-atom-thick sheet of carbon that is extremely strong and conducts electricity well, is the thinnest material ever made. Researchers believe that it could be used as a transparent electrode in photovoltaic cells, replacing a layer of indium tin oxide (ITO) that is brittle and becoming increasingly expensive.

Wee Shing Koh of the A*STAR Institute of High Performance Computing in Singapore and co-workers have compared these two materials. They found that graphene outperforms ITO when used with solar cells that absorb a broad spectrum of light

The wavelengths of light from the Sun have a range of intensities and deliver varying amounts of power. To maximize a photovoltaic device's performance, its transparent electrode should have a low electrical resistance, while also transmitting light of the right wavelengths for the cells to absorb.

Square sheets of graphene produced by today's chemical vapor deposition technology have an electrical resistance roughly four times that of a typical 100-nanometer-thick layer of ITO. Although adding more layers of graphene reduces its resistance, it also blocks more light. Koh and his co-workers calculated that four layers of graphene stacked together had the best chance of matching ITO's performance.

Graphene has one key advantage over ITO: it allows more than 97% of light to pass through to the solar cell beneath, regardless of its wavelength. In contrast, ITO tends to block certain wavelengths more than others. Four-layer graphene is slightly more transparent at near-infrared wavelengths than ITO is, for example.