A team led by Nakita Noel of Oxford University’s Department of Physics has demonstrated that the lead in solar cells based on lead halide perovskites can be replaced with tin, dramatically driving down the cost of commercial solar cells.

Researchers have already achieved 17 percent efficiency after two years with perovskite solar cells. Now, a protoype of the first lead-free perovskite solar cell has achieved an efficiency of just six percent, but the team believes that efficiencies over 20 percent could be achieved if the core material is made more stable.

Tin perovskite cells would be far less costly to mass produce and would make the disposal of solar cells less of an issue. While the amount of lead in current solar cells is small, it nevertheless raises both environmental and public health concerns.

“We wanted to try and replace the lead with something similar but non-toxic. Tin has been reported in perovskites before, but not in a solar cell, so we decided to see if it would work. We found that by using tin we managed to keep everything that is good about lead in a solar cell but use a metal that is safe, cheap, and abundant,” said Noel in a statement.

The prototype lead-free material displayed a tendency to degrade in the presence of oxygen and moisture. To avoid this problem, the researchers prepared and sealed the tin materials in a nitrogen environment and are confident that they can fully stabilize the material given time.

If the researchers are successful, their work could provide a cheap alternative that is as efficient as silicon-based solar cells that are non toxic and easier to mass produce.

“The demonstration of solar cells using tin-based perovskites is a clear indication that good solar cell operation is not unique to lead, and therefore also opens up the use of other similar metals in the perovskite structure, leading to a multitude of new research avenues for optimising these materials,” said team leader Henry Snaith.

The researchers may get some help from a team at Northwestern University who have also developed a tin-based perovskite solar cell. That team, lead by Mercouri G. Kanatzidis, Professor of Chemistry in the Weinberg College of Arts and Sciences, has created a solid-state tin solar cell that an efficiency of just below six percent.

“Other scientists will see what we have done and improve on our methods. 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,” said Kanatzidis in a statement.

Solar energy is clean, with zero emissions and does not require the same amount of space as other alternative such as wind. Over the last few decades it has become the leading green energy source. Since 1995, global solar energy capacity has grown from less than one gigawatt to over 100 gigawatts, according to Cleantechnica.com. However, the cost of solar cells, which is partially due to the toxic lead content, has prevented solar energy from reaching its full potential.

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

The work of the Oxford researchers is documented in the journal Energy & Environmental Science. The Northwestern University work can be found in the journal Nature Photonics.