Invisible wires could improve solar efficiency

Scientists have found a way to improve solar cell design, improving efficiency and lowering the cost of solar cells.

Currently, the design of solar cells means some sunlight is reflected away from the semiconductor, reducing the efficiency of the cell to convert sunlight into electricity.

To solve this problem, Stanford researchers moulded silicon nanopillars along with a gold metal layer to the semiconductor silicon layer below. The researchers compared this to a colander with tiny funnels above the holes to enable most of the water to flow through with no problem.

Optical analysis of the 16nm gold film before the nanopillars were added showed 50% of incoming light was reflected away. When coated with an anti-reflection layer after the nanopillars were added to the gold film, broad band absorption of up to 97% was observed, said the researchers.

Lead author Vijay Narasimhan, said: “Essentially what our structure does, the nanopillars act as funnels that capture light and guide it into the silicon substrate through the holes in the metal grid.

“Solar cells are typically shaded by metal wires that cover 5 to 10 percent of the top surface. In our best design, nearly two-thirds of the surface can be covered with metal, yet the reflection loss is only 3 percent. Having that much metal could increase conductivity and make the cell far more efficient at converting light to electricity,” he added.

The researchers believe this could boost the efficiency of a typical solar cell to 22%.

The new technology can also be used with other semi conducting materials for other purposes such as photosensors, light emitting diodes, displays and transparent batteries.

Study co-author Yi Cui said: “With most optoelectronic devices, you typically build the semiconductor and the metal contacts separately. Our results suggest a new paradigm where these components are designed and fabricated together to create a high-performance interface."

The research was published in ACS NANO.