Green future for solar cells

Scientists from the University of Cambridge have proposed a green alternative to producing next-generation solar cells.

Using both theoretical and experimental methods, the researchers have shown that bismuth, next to lead on the periodic table, could be used in low-cost solar cells. Although the majority of solar cells are silicon, a rising number are being produced from a new material called hybrid lead halide perovskites.

Environmental safety

However, perovskite solar cells are viewed warily due to lead being an integral part of their composition. Scientists are looking for non-toxic materials that can replace the lead in these solar cells without affecting their performance.

Dr Robert Hoye, from Cambridge’s Cavendish Laboratory and the lead author of the paper, 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.”

Bismuth oxyiodide was the focus for Dr Hoye’s investigation. It had previously been considered for use in solar cells and water splitting but suffered from low-efficiency rates and degradation in liquid electrolytes. Researchers tested bismuth oxyiodide's role in solid-state solar cells and found it was as defect tolerant as lead halide perovskites and more stable in air than some lead halide perovskite compounds. By sandwiching bismuth oxyiodide between two oxide electrodes they were able to demonstrate a record performance, converting 80% of light to electrical charge.

As bismuth-based devices can be made with common industrial techniques, they can be produced at scale at low cost. Professor Judith Driscoll, also from the University of Cambridge, and co-author of the paper, said: “Bismuth oxyiodide has all the right physical property attributes for new, highly efficient light absorbers. I first thought of this compound 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.”

The research, which involved scientists from MIT, was published in Advanced Materials.