Scientists at the University of Oxford (UK), working with colleagues from Wuhan University (China), have identified bismuth sulfide (Bi₂S₃) as a semiconductor that sidesteps a fundamental trade-off between light absorption and charge carrier lifetime. The team estimates that charge recombination in this material occurs approximately 75% more slowly than in conventional semiconductors with equivalent light absorption.
Key points:
- Material — bismuth sulfide (Bi₂S₃), an earth-abundant and non-toxic semiconductor.
- The novel mechanism reduces the rate of charge carrier loss by approximately 75% compared to conventional materials with equivalent light absorption.
- Method — ultrafast terahertz spectroscopy of thin films across a wide temperature range, from room temperature to near absolute zero.
- Publication — Nature, October 28, 2026 (DOI: 10.1038/s41586-026-11223-x).
The trade-off that bismuth sulfide overcomes
Photovoltaics has long contended with an inconvenient pattern: materials that absorb sunlight more intensely typically convert that captured energy into electricity less efficiently. The culprit is rapid recombination of electrons and “holes,” which consumes a portion of the collected carriers before they can reach the electrodes. According to techxplore.com, the team led by Professor Laura Herz of Oxford’s Department of Physics (corresponding author) and Professor Marina Filip, whose group carried out the electronic structure calculations, found that Bi₂S₃ possesses an unusual band structure with densely packed energy levels. It is precisely this feature that allows the material to combine strong light absorption with slowed recombination — a combination long considered difficult to achieve.
A “temporary reservoir” for charge carriers
In the proposed model, light-excited charges rapidly settle into lower-energy states that act as a temporary reservoir. Carriers reside there longer and are lost more slowly, so a greater fraction can be collected by the external circuit. To measure the charge dynamics, the researchers applied ultrafast terahertz spectroscopy to thin films of the material across a broad temperature range — from room temperature to near absolute zero. The resulting estimate is a roughly 75% reduction in the rate of charge carrier loss compared to conventional materials with equivalent light absorption.
Why this material stands out
Bismuth sulfide is an earth-abundant and non-toxic semiconductor. The authors themselves are measured about the implications: Laura Herz stresses that the work “demonstrate[s] a physical mechanism rather than a finished solar cell.”
What this could change for photovoltaics
If another class of semiconductors can genuinely deliver both strong absorption and long carrier lifetimes simultaneously, developers gain an additional lever for improving solar panel efficiency — without the delicate compromise between layer thickness and losses within it. The discovery broadens the roster of semiconductors worth considering beyond familiar silicon and perovskites — a field where there is an intense ongoing search for new materials for affordable solar panels.
For readers tracking what will define the next generation of solar modules, this is a significant fundamental result: it shows that the absorption-versus-carrier-lifetime trade-off is not absolute, and that the physics of a specific material can circumvent it. Whether bismuth sulfide will underpin mass-produced panels depends on future work assessing the efficiency and durability of complete cells, not just individual thin films. For now, it is worth following further publications from the Herz and Filip groups and watching for attempts by other laboratories to reproduce the identified mechanism in their own samples.
Sources: TechXplore, Nature (DOI)
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