Professor Laura Herz and Professor Marina Filip

A study led by Professor Laura Herz, Supernumerary Fellow in Physics at Univ and Professor of Physics, and supported by Professor Marina Filip, Tutorial Fellow in Physics and Professor of Condensed Matter Physics, has identified a new semiconductor that addresses a key challenge in the field of light-harvesting materials. This discovery could allow the development of solar panes with greater efficiency and higher output.

Materials with a greater capacity to absorb light are often less able to transform that light into electricity as they lose their electrical charges quickly. This is one of the key obstacles currently facing those working with solar energy and has limited the rate at which solar cells transform sunlight into electricity.

A new study led by Professor Herz has highlighted how bismuth sulfide appears to circumvent this tendency due to an unusual arrangement of energy levels that allow strong light absorption and slow loss of electrical charge. The results of the study, which have been published in Nature, indicate a novel way to design solar cells with greater efficiency.

During the study, researchers treated thin films of bismuth sulfide with incredibly short laser pulses before measuring the speed at which the charges dissipated using a technique known as ultrafast terahertz spectroscopy. They then took measurements at temperatures varying from just absolute zero to room temperature.

Professor Filip’s group in the Department of Physics were also able to carry out electronic structure calculations to highlight the rare qualities of bismuth sulfide. They found that it absorbs light through a stronger route but loses charges through a slower, weaker route. The two routes are so close in energy that charges spend time in lower-energy states which act as a reservoir and slow their loss.

Professor Herz, corresponding author on the paper titled “Delayed electron–hole recombination in a pseudo-direct semiconductor”, said, “What makes this discovery particularly exciting is that we are not simply improving an existing semiconductor property but identifying a different way in which semiconductors can behave. Understanding this mechanism gives us a roadmap for discovering and potentially engineering other materials with similarly advantageous properties.”

The discovery could benefit solar energy in two ways. Longer-lasting charges are more likely to be collected, potentially reducing energy loss in solar cells while maintaining strong light absorption. Additionally, charges with a longer life have the potential to provide more time for chemical reactions required to convert sunlight into fuels. The calculations made by the team suggest that screening materials databases could lead to the discovery of other materials with the same property, and that similar materials could be engineered,

Now that the team has highlighted this physical mechanism, there is a need for further work to translate their findings into more optimal solar cell technologies.

The research was an international collaboration between Wuhan University in China and the University of Oxford. It was funded by the UK Engineering and Physical Sciences Research Council (EPSRC) with additional support from the Italian Ministry of University and Research and Oxford Photovoltaics.

Published: 12 November 2026

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