Study says bismuth could replace lead in perovskite solar cells

A new study has shown that bismuth, a heavy metal known as the “green element”, could be used as a non-toxic alternative to lead in the development of perovskite solar cells.

Researchers from the University of Cambridge and their colleagues at the Massachusetts Institute of Technology (MIT), the National Renewable Energy Laboratory (NREL) and the Colorado School of Mines in the US have been trying to determine whether bismuth could replace the lead in perovskite solar cells without negatively affecting performance. Their work has helped another research group estimate that bismuth-based cells could convert light into energy at efficiencies of up to 22%.

After using theoretical and experimental methods, the Cambridge and US researchers have found that the bismuth oxyiodide (BiOI) compound is as tolerant to defects as lead halide perovskites, and could very well be the sought non-toxic alternative.

“I first thought of this compound [bismuth oxyiodide] around five years ago, but it took the highly specialised experimental and theoretical skills of a large team for us to prove that this material has real practical potential,” said co-author Judith Driscoll, of the Department of Materials Science and Metallurgy at Cambridge.

A device developed by the team was able to convert 80% of light to electrical charge by sandwiching the bismuth oxyiodide light absorber between two oxide electrodes.

David Scanlon, a theorist at University College London (UCL), who was not involved in this work, said: “When I saw this work, my team calculated based on the optical properties that bismuth oxyiodide has a theoretical limit of 22% efficiency, which is comparable to silicon and the best perovskite solar cells.”

Bismuth-based devices can be made using common industrial techniques so they could be produced at scale and at low cost.

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