For years, scientists have tried to exploit the potential of sunlight as a source of energy. Hence the development of solar cells, which can be found in our everyday life from the small calculators to enormous charging stations for electronic vehicles.

Recently, in a bid to revive photovoltaics as one of the possible energy generators in today's world, a unique type of solar cell emerges anew. It uses tin instead of the traditional lead perovskite as the "harvester of light," earning it the title as the "next big thing" in the industry of solar energy.

The environment-friendly solar cell is first developed by a group of researchers at the Northwestern University in Illinois, who discovered that the newfound solar cell can be safely used with "bench" chemistry or the conventional method where scientists do the chemical mixing manually.

Bench chemistry is sometimes risky, as some of the chemicals needed to be combined together may be hazardous to humans. Take lead for example. First versions of solar cells are made of lead perovskite. Lead has been found to be a toxic element, and it is poisonous if ingested or inhaled.

Since the newly-developed solar cells are made of tin-based perovskite that exhibits similar efficiency with the lead-based one, they absorb light just the same in a sandwich of two electric charge transport layers, which make them purely safe to use.

Moreover, tin-based ones tend to absorb most of the visible light spectrum, while the salt in perovskite can be dissolved and come back to normal state even without heating, the scientists said.

"This is a breakthrough in taking the lead out of a very promising type of solar cell, called a perovskite," said lead author of the study Mercouri G. Kanatzidis, a Charles E. and Emma H. Morrison Professor of Chemistry in the Weinberg College of Arts and Sciences. "Tin is a very viable material, and we have shown the material does work as an efficient solar cell."

While tin and lead belong to the same group in the table of elements, the lead-free solar cell already recorded an efficiency of six percent, which the researchers considered as "a very good starting point."

Such solar cells are not new-fangled since most of them have been assembled as early as 2008, but the researchers' breakthrough reinforced tin's potential as a solar cell material. Not only it is safe for human use, it is also safe for the environment, not to mention the high costs in it production.

"Solar energy is free and is the only energy that is sustainable forever," Kanatzidis explained. "If we know how to harvest this energy in an efficient way we can raise our standard of living and help preserve the environment."

The sun's rays give off an estimated 1,000 watts of energy per square meter of the Earth's surface, enough to power our appliances at home. Should the so called "solar revolution" push through, electricity in every household would be free of charge.

The study was published in the journal Nature Photonics.