A joint team of researchers at the University of Cambridge and from the US have found new material which can replace the use of lead in solar cells with bismuth.

The study has been conducted by a collaboration of team which includes scientists from the Massachusetts Institute of Technology (MIT), the National Renewable Energy Laboratory (NREL) and Colorado School of Mines in the US and the University of Cambridge.

Results from the study have been published in the journal Advanced Materials and they suggest that solar cells which will use bismuth can replicate the properties displayed by lead-based solar cells, but without any concern for toxicity.

Studies from another research group stated that bismuth-based solar cells can go beyond lead-based solar cells in terms of efficiency, reaching up to 22%, which is comparable to the most highly advanced solar cells that are available in the market today.

Although, solar cells are made from silicon, yet silicon needs to have high levels of purity, in order to convert light into energy. Such high levels of purity require several stages of processing, which can ultimately increase the cost of production.

Hence, scientists found a way to use lead halide perovskite material, which does not require such high levels of purity, as silicon, hence they can be produced at relatively low costs. But, lately the safety of lead has been a concern.

In the lead halide perovskite-based solar cells, lead is an integral part in the chemical structure of the material. The presence of lead in the solar cells is still debatable in the scientific community, in terms of its safety towards humans, animals and environment is concerned.

Bismuth is of interest in the study as it is also a heavy metal like lead and unlike lead it is non-toxic. Bismuth can be found in cosmetics, personal care products and medicines.

The study looked at the possibility of using bismuth oxyiodide, a material which was previously investigated for its use in solar cells and water splitting.

The study found that the material is tolerant to defects like lead halide perovskites. The material is claimed to have been stable in air for at least 197days. By sandwiching the bismuth oxyiodide light absorber between two oxide electrodes, the team demonstrated that the device can convert 80% of light to electrical charge.

Cambridge’s Cavendish Laboratory and Department of Materials Science & Metallurgy, and the paper’s lead author Dr Robert Hoye said: “We wanted to find out why defects don’t appear to affect the performance of lead-halide perovskite solar cells as much as they would in other materials.

“If we can figure out what’s special about them, then perhaps we can replicate their properties using non-toxic materials.”

Image: Scientists find new material to replace lead-based solar cells. Photo: Courtesy of University of Cambridge.