Researchers at the University of Oxford, working with Wuhan University, have identified a mechanism in bismuth sulfide that sidesteps a classic solar-cell dilemma: materials that absorb light strongly usually lose the electrical charges they generate very quickly. The study, published in Nature on 28 October 2026 as “Delayed electron-hole recombination in a pseudo-direct semiconductor”, shows the material combining strong absorption with slower charge loss.
The secret lies in its energy-level arrangement. Bismuth sulfide absorbs light through a strong route between energy levels, but just below it sits a second, much weaker route that acts as a temporary reservoir: charges spend much of their time in these lower-energy states, where they recombine slowly. That stockpile gives charges more time to be collected before they are lost.
To test the idea, the team excited thin films of the material with extremely short laser pulses and tracked how fast the charges disappeared using ultrafast terahertz spectroscopy, from room temperature down to just above absolute zero. Unlike the usual behaviour, in which cooling speeds up loss, in bismuth sulfide the loss slowed as it cooled — exactly what is expected if more charges were settling into the reservoir. Electronic-structure calculations by Professor Marina Filip's group at Oxford support the same explanation.
At room temperature, the team estimates a reduction of about 75% in the charge-loss rate compared with conventional materials that absorb light just as strongly. Note the number carefully: this is not a 75% increase in solar-panel efficiency, but a lower loss rate in the physical mechanism. The work demonstrates a mechanism in thin films, not a finished panel with a new efficiency record — turning the principle into practical devices, and finding other materials with the same property, is the next challenge. The corresponding author is Professor Laura Herz of Oxford's Department of Physics.
Image credit: Laura Herz / University of Oxford, via Knowridge.
Fontes
- Tech Xplore: Semiconductors could sidestep a key solar-energy trade-off
- Knowridge: Scientists uncover a new way to cut solar energy losses
- Solar Cell: Oxford study finds bismuth sulfide absorbs light strongly but holds its charges longer
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