Scientists break Shockley-Queisser efficiency limit for silicon solar cell in experiment

From pv magazine Global

Researchers from the University of Delaware in the United States and Taizhou University in China claim to have achieved a record power conversion efficiency of “50%–60%” in a silicon solar cell by inhibiting the lattice atoms’ thermal oscillations at extremely low temperatures.

“For our experiment, we used pieces of commercial PV cells,” the research’s lead author, Bingqing Wei, told pv magazine. “We had to put the 4 mm x 8 mm cells inside a low-temperature chamber that is not big enough to hold an entire cell.”

If confirmed, this result may be the “first experimental breach” of the upper theoretical limit of energy absorption efficiency for silicon solar cells, called the Shockley-Queisser limit, which is about 33.7%.

“So far, we have confirmed the results internally,” Wei went on to say. “The testing was conducted at extremely low temperatures, which prevented us from finding a third party who could do the experiments and certify the results.”

The scientists explained that the record efficiency was achieved at very low temperatures of 30–50 Kelvin (K), which are a few tens of degrees above absolute zero. They also noted that, below 150 K, conventional solar cells collapse as energy carriers become trapped.

“When the temperature is less than 150–200 K, the efficiency will decrease with decreasing temperature due to the effects linked to carriers. The hypothesis that increasing efficiency by cooling no longer applies at low temperatures appears to challenge the law of thermodynamics,” they also stressed, noting that this freeze-out effect can result in a strong short-circuit current reduction and a nearly zero efficiency at extremely low temperatures.

“The traditional theory may face challenges when applied to solar cells operated at extremely low temperatures,” they added.

Below 150 K, free charge carriers in solar cells collapse, but photocarriers remain unaffected by the freeze-out effect and could survive even at zero K if photons are available. The photocarrier density of the bottom cell layer is determined by the light intensity reaching it, which means the freeze-out effect can be overcome by enhancing light penetration depth and decreasing the cell thickness.

Their strategy consisted of enhancing the light penetration depth to effectively mitigate carrier freeze-out while reducing thermal losses, which reportedly expanded the operational temperature range of silicon cells to 10 K. They used homochromatic lasers with different photon energies to increase carrier mobility through temperature regulation.

Under standard illumination conditions and at a temperature of 30 K, the cell reached an efficiency of around 51%, which the scientists said doubled the 27.3% world-record efficiency achieved at room temperature by Chinese manufacturer Longi for a heterojunction back contact (BC) solar cell and is around 20% higher than the S-Q limit at the same temperatures.

The experimental results were presented in the study “Surpassing Shockley–Queisser Efficiency Limit in Photovoltaic Cells,” published in Nano-Mirco Letters. “This work rewrites the low-temperature PV playbook, turning the once-dreaded freeze-out regime into an ultra-efficiency window—pointing toward over 50% single-junction devices for extreme-environment energy harvesting.”

Looking forward, the research group intends to develop 4 cm² “flight-style” cells that could be used for space applications and to qualify for NASA Commercial Lunar Payload Services.

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