Solar waffles trap light

17 Jun 2002

Thin solar cells may cut costs without loss in efficiency.

Solar waffle

Waffle-shaped solar cells only 15 µm thick can produce as much solar power as conventional 300 µm thick cells, say researchers in Germany. The solar cell has a surface that is textured with periodically positioned inverted pyramids that trap light by total internal reflection. This contains the light within the well and maximizes the absorption of sunlight.

The thin solar waffles are produced by a technique known as the porous silicon (PSI) process. The required pattern is etched into a silicon substrate surface and is then coated with a porous silicon layer. Single crystalline silicon is then grown epitaxially on the porous layer and removed using a glass superstrate. This process does not require any complex processing steps and the initial patterned substrate can be reused.

Rolf Brendel of the Center for Applied Energy Research in Erlangen explained the main advantage of this process: "Because we are using thin silicon there is a potential to save on material costs while sacrificing little efficiency."

At present, the researchers observe similar efficiencies to conventional cells. "Enhancing the efficiency while keeping the cell process as simple as it is now remains our priority," Brendel told Optics Org. Conventional cells have a thickness of approximately 300 µm and, although thinner, the solar waffle cells convert sunlight to solar power by the same process.

The main market for this technology is consumer products such as palm tops and other small devices that require high-power conversion efficiencies. The solar waffle is also suitable for supplying electricity to satellites in space because thin silicon modules can withstand cosmic radiation for a longer period of time.

The researchers are now developing periodic and random waffle structures with thicknesses of less than 10 µms. New machines are also being developed to optimize and reduce the costs of the epitaxy process. "There is a long way to go to compete with conventional technology. We can however reduce material consumption dramatically," said Brendel.