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Tin-made solar cells are cost effective alternative to lead

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Solar cells made from tin could be a cost-effective alternative to new models based on lead, becoming an environmentally-friendly power source. Lead is used in laboratory solar cells to absorb sunlight, in tests of the next generation devices. 

Northwestern University researchers designed the new solar cell. These can be created using simple chemical processes and without the use of hazardous materials. 

Mercouri Kanatzidis, an inorganic chemist, led the research into tin as a possible component in solar cells. 

Lead components in the most modern laboratory solar cells are formed into what is called a perovskite structure. The new energy-gathering technology uses this same formation using tin in place of the toxic metal. These materials, first developed in 2008, may revolutionize solar cell technology. 

Lead perovskites are capable of converting around 15 percent of the light that strikes them into electricity. Researchers hope their new development will allow tin to rival or even surpass those efficiency levels. Initial tests reported just 5.73 percent from the new cells. 

"Further efficiency enhancements are expected following optimization and a better fundamental understanding of the internal electron dynamics," researchers wrote in an article announcing the results of their investigation. 

Tin has a couple big advantages over lead as a material for solar cells. The perovskite salts can be dissolved, unlike lead. Afterward, they can be recovered from solution without heating. Second, the material can absorb light over a wider range of wavelengths than lead. 

"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," Kanatzidis said.

The new cells are composed of five layers. The top layer is composed of electrically-conducting glass. Under this is a layer of titanium dioxide, then the tin perovskite layer to conduct electricity. An essential "hole transport" layer was placed under this, composed of pyridine, a chemical related to benzene. The bottom layer is gold, to conduct and transmit electricity. 

"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," Robert P. H. Chang, a nanoscientist at the university, said in a press release announcing the discovery. 

The entire cell is less than 0.00008 inches thick. Solar cells installations are becoming more and more common worldwide, as nations work to fight global climate change. 

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