When people talk about solar photovoltaics, they’re usually talking about silicon PV, which has dominated the solar industry for decades, but there are a number of competing technologies out there that are trying to give traditional crystalline silicon-based PV a run for its money and one of the most promising is perovskite crystal technologies. Such technologies are becoming more competitive with silicon PV in terms of efficiency and manufacturing costs.
Perovskite crystals are materials that have the same structure as calcium titanate and can absorb sunlight in PV cells. However they’re much cheaper to produce than crystalline silicon PV. In fact, perovskite-based solar cells could be used with silicon solar cells to create a PV cell that could theoretically reach 32 percent efficiency. Even without silicon, they could produce PV cells and modules that are much less expensive than silicon PV.
Until now though most perovskite PV cells have used lead, which has numerous drawbacks, like being horrible for the environment and causing brain defects in children, etc. Yesterday and last week two universities, Northwest University in Chicago and Oxford University in Great Britain, respectively, both said they had developed perovskite PV cells with inexpensive and environmentally friendly tin instead of lead.
Both Northwestern and Oxford claim to have created the first Perovskite crystal solar cells without lead and both are publishing papers on it in different journals. Northwestern published in Nature Photonics and Oxford is publishing in Energy & Environmental Science. Both universities produced cells with efficiency levels near 6 percent and both theorized that they could reach much higher efficiencies.
“This is a breakthrough in taking the lead out of a very promising type of solar cell, called a perovskite,” said Mercouri Kanatzidis, Northwestern’s Charles E. and Emma H. Morrison Professor of Chemistry. “Tin is a very viable material, and we have shown the material does work as an efficient solar cell.”
Kanatzidis developed, synthesized and analyzed the material. He patterned with Professor Robert Chang, a materials science and engineering and nanoscientist, to engineer the solar cell. “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,” Chang said.
“Two things make the material special: it can absorb most of the visible light spectrum, and the perovskite salt can be dissolved, and it will reform upon solvent removal without heating,” the university said.
“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.”
Across the pond, Oxford seems to have taken a similar approach. “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,” said Nakita Noel of Oxford University’s Department of Physics, first author of the paper. “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.” Oxford’s researchers anticipated creating a perovskite cell that could be more than 20 percent efficient if the material can be made more stable.