From: Robin Blackstone, ENN
Published May 5, 2014 10:16 AM

New hopes for getting the lead out of solar

Solar energy is arguably our most viable low cost energy source. It is forever sustainable and easily captured and converted. But now the technology may have taken yet another leap forward. To date the foundational technology behind photovoltaics was a structure called perovskite, which has been made with lead. Using tin instead of lead perovskite as the harvester of light, a team of Northwestern University researchers has created a new solar cell with "good efficiency". This good efficiency solar cell is low-cost, environmentally friendly and can be easily made using "bench" chemistry -- no fancy equipment or hazardous materials.

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"This is a breakthrough in taking the lead out of a very promising type of solar cell, called a perovskite," said Mercouri G. Kanatzidis, an inorganic chemist and tin expert. "Tin is a very viable material, and we have shown the material does work as an efficient solar cell."

Solar cells have typically used a structure called a perovskite made with lead as the light-absorbing material. The new solar cell is made with tin instead. Lead perovskite has achieved 15 percent efficiency. It is expected that tin perovskite will reenergize the field by matching and possibly surpassing that efficiency making them the "next big thing in photovoltaics".

Kanatzidis developed, synthesized and analyzed the material and then turned to Northwestern collaborator and nanoscientist Robert P. H. Chang for help in engineering a solar cell that worked well.

"Our tin-based perovskite layer acts as an efficient sunlight absorber that is sandwiched between two electric charge transport layers for conducting electricity to the outside world," said Chang. Details of the lead-free solar cell will be published May 4 by the journal Nature Photonics.

Kanatzidis touts their solid-state tin solar cell efficiency rating of just below 6 percent as a very good starting point. Two things make the material special: it can absorb most of the visible light spectrum, and the perovskite salt can be dissolved reforming upon solvent removal without heating.

"Other scientists will see what we have done and improve on our methods," Kanatzidis said. "There is no reason this new material can't reach an efficiency better than 15 percent, which is what the lead perovskite solar cell offers. Tin and lead are in the same group in the periodic table, so we expect similar results."

Perovskite solar cells have only been around -- and only in the lab -- since 2008. In 2012, Kanatzidis and Chang reported the new tin perovskite solar cell with promises of higher efficiency and lower fabrication costs while being environmentally safe.

Read more at Northwestern University.

Solar Panel image via Shutterstock.

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