A new type of tandem solar cell for space could double efficiency

The new nanowires are light and require a small amount of material, meaning they will soon be tested on satellites that already use traditional solar cells. In fact, as per a press statement from Lund University, they were sent up to space a few days ago.

The new type of solar cells could double the efficiency

The photovoltaic nanowires feature three different band gaps. This means they use three different materials that react to different wavelengths of solar light. This means they are, in theory, a better match for the solar spectrum than today’s silicon solar cells.

The scientists behind the new type of nanowires published their findings in the journal Nano Research. Their paper outlines work that has taken years to complete. “The big challenge was to get the current to transfer between the materials. It took more than ten years, but it worked in the end,” explained Magnus Borgström, professor of solid state physics, who wrote the articles with former doctoral student Lukas Hrachowina.

Scientists are increasingly researching solar cells with different band gaps, known as tandem solar cells, as these could greatly improve efficiency. Some research suggests it could roughly double the efficiency of today’s commercial silicon solar cells.

“Silicon solar cells have soon reached their maximum limit for efficiency. Therefore, the focus has now shifted to developing tandem solar cells instead. The variants fitted on satellites are too expensive to put on a roof,” Borgström said.

Nanowires are like a “sparse bed of nails”

Tandem solar cells are typically developed by synthesizing different semiconducting materials on top of one another. The researchers from Lund have come up with a unique method where they develop extremely thin rods of semiconducting material on a substrate. This allows them to use a small amount of material per unit area, which reduces costs and also makes it a more sustainable method.

The three materials used in nanowires are indium, arsenic, gallium, and phosphorus. Using these materials, the scientists were able to achieve an efficiency of 16.7 percent, though they believe this could rise to roughly 47 percent using the same structure with more band gaps.

Aside from being more efficient, the nanowires also possess the durability required for space travel. “A sheet of nanowires can be likened to a very sparse bed of nails,” Borgström explained. “If some aggressive protons came along, which happens now and then, they would probably land between the wires, and if they happened to eliminate some wires, it would not matter very much. The damage could be worse if they land on a regular thin film.”

To put their materials to the test, however, the scientists have fitted a research satellite with their nanowire solar cells. Their satellite was recently lifted to space by partners at the California Institute of Technology, Caltech, in the USA. The satellite will be in orbit in spring, and the scientists say they will continually receive data on the performance of their nanowires.