New solar cell design could convert 60% of sunlight into energy

It took the team 15 years to build the first solar cell using these Gap and Ti but could change solar energy industry in the future.

Ameya Paleja

Solar cells made from different materials could unlock solar energy potential.

bombermoon/iStock

In a world-first, researchers at the Universidad Complutense de Madrid in Spain have fabricated an intermediate band (IB) solar cell using gallium phosphide and titanium that could potentially deliver an energy conversion efficiency of 60 percent.

The solar cell could deliver this performance at a wavelength of 550 nm and above.

To harness energy from the brightest star in our skies, we have deployed solar cells that can convert sunlight into electric current. The silicon-based solar cell, however, can only harness a part of the sunlight incident on it, giving off the rest as heat.

The upper limit on how much energy a solar cell can convert into electricity is Shockley Queisser (SQ). Theoretically, it can be computed taking into account the energy of the photon on a single p-n junction and losses seen in a solar cell.

The SQ limit of a solar cell is subject to the material used to make it. For silicon, the bandgap is 1.3eV, and the SQ limit is 33.7 percent. This effectively means that under the best-case scenario, even the highest-quality solar cell ever produced will still not be able to harness 77.3 percent of the sunlight incident on it.

To meet our increasing energy demands, we would need to build more solar panels and cover more areas of the planet with them. However, a solar cell made with a different material could have a higher SQ limit, making electricity generation more efficient.

Javier Olea Ariza and his team of researchers at Universidad Complutense de Madrid have been working for over 15 years with gallium phosphide (Gap) and titanium (Ti) in an attempt to make a more efficient solar cell.

Since the SQ limit is dependent on the bandgap of the semiconductor material, Ariza and his team chose Gap, which has a bandgap of 2.26 eV. The team built a one cm2-sized solar cell with a Gap: Ti absorber no thicker than 50 nm and metal contacts using gold and germanium.

Through a series of experiments in transmittance and reflectance measurements, the team found that the solar cell had a broad band due to enhanced light absorption at wavelength above 550 nm. This is likely due to the use of Ti in the setup. The theoretical potential of the structure is around 60 percent.

The team first worked with these materials in 2009, but it took them 15 years to build the first devices with them. Even at this point, the device is not close to being deployed in the field. Its efficiency is very poor, and much work remains to be done.

The team first wants to make a prototype solar cell and demonstrate higher efficiency. They also intend to sort issues with solar cell construction by using different approaches to incorporating Ti in the future.

Commercial deployment of this technology could take a long time, but we are no longer limited by solar cells’ potential.

The research findings were published in the journal Materials Today Sustainability.

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Ameya Paleja Ameya is a science writer based in Hyderabad, India. A Molecular Biologist at heart, he traded the micropipette to write about science during the pandemic and does not want to go back. He likes to write about genetics, microbes, technology, and public policy.

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