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The researchers discovered why the presence of selenium, especially in solar cells, improves efficiency, a breakthrough that could be exploited to further strengthen solar technology.
Led by Tom Fiducia, a Ph.D. student at Loughborough University, the work aimed to establish the mechanism by which selenium improves the performance of solar panels in cadmium telluride (CdTe). According to the paper, which appears in Nature EnergyCdTe panels are currently producing the cheapest form of available solar energy, undercutting hydrocarbons in many parts of the world.
By combining selenium with the CdTe absorber, cell efficiency has increased from 19.5% to its current record of 22.1%. It was previously known that the presence of selenium helped to reduce the bandgap of the absorbent material, thus increasing the short circuit current of the cell, but this did not fully explain the efficiency gains. However, by measuring the amount of light emitted by the panels, the team was able to solve the puzzle. Selenium provides higher luminescence efficiency and longer diffusion lengths in the alloy material, thereby overcoming critical defects in the bulk of the absorbent layer.
"Although it sounds counterintuitive, a good defect-free solar cell material is very effective at emitting light and therefore highly luminescent," Fiducia said.
"We mapped the luminescence emitted by a solar cell containing selenium at a resolution of about 1/10 000th millimeter and compared it to a similar high-resolution map of the selenium concentration taken on the same area of the cell. It is striking that data indicating that selenium-rich regions are luminescent are much brighter than pure cadmium telluride and the effect is remarkably powerful. "
According to Fiducia, now that the mechanism behind the gains has been highlighted, it could be leveraged to deliver even better CdTe cell performance, which could potentially make solar energy even less expensive at worldwide.
"Now that the improvement in selenium-induced efficiency is better understood, it may be possible to use this knowledge to further increase the effectiveness of telluride-based solar panels." cadmium, "he said.
"For example, this could be simply by increasing the amount of selenium in the devices or by changing its distributions in the cell. If efficiency could be improved, it would lower electricity prices and have a direct positive impact on the regions adopting the technology. "
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