Nano-technique could make solar cells less “shiny” and more efficient

Solar cells consist of a semiconductor sandwiched between metal contacts that carry the electrical current. However, the shiny metal on the top of the cell hampers its efficiency by reflecting sunlight away from the semiconductor.

The Stanford team, which was led by graduate student Vijat Narasimhan, has used nanotechnology to make this upper contact invisible to incoming light.

In most solar cells, the upper contact consists of a metal wire grid that carries electricity to or from the device. But these wires also prevent sunlight from reaching the semiconductor, which is usually made of silicon.

For the study, the Stanford team placed a 16-nanometer-thick film of gold on a flat sheet of silicon. The gold film was riddled with an array of nanosized square holes, but to the eye, the surface looked like a shiny, gold mirror.

Optical analysis revealed that the perforated gold film covered 65 per cent of the silicon surface and reflected, on average, 50 per cent of the incoming light. The scientists reasoned that if they could somehow hide the reflective gold film, more light would reach the silicon semiconductor below.