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Solar energy is a viable alternative to fossil fuels. A solar cell converts sunlight into electricity. The conversion efficiency isn't enough to enable widespread applications of solar cells.
A fundamental limit to the maximum efficiency of the devices is given by their temperature and entropy. The Landsberg limit is imposed by the blackbody radiation that is attributed to sunlight. The Landsberg limit is the most general limit for the efficiency of sunlight.
The Shockley-Queisser (SQ) limit is based on the law of Kirchhoff, which states that the emissivity should be equal for any photon energy. The principle of detailed balance has governed solar cell operation for decades. One way to break the time reversal symmetry is to allow light to travel only along one direction. The SQ limit can be surpassed if the PV converter absorbs more and emits less radiation.
Researchers from the US Army Research Laboratory and Texas A&M University propose a way to break the limit by using nonreci.
A single-cell photovoltaic design integrated with nonreciprocal optical components can provide a 100 percent reuse of the emitted radiation by the same cell due to nonreciprocal photon recycling. This is a different design than the previous one, in which the light emitted by one cell was absorbed by another, and the cells were arranged in such a way that the light was absorbed by another.
Sergeev and Sablon discuss sunlight in terms of coherence, relativity, nonequilibrium distributions, disorder, information, and negentropy after the seminal works of Von Laue, Einstein, and Brillouin. The authors observe that the sun's rays are not strongly disordered and that the light moves along straight lines in a narrow angle. The observation suggests that the conversion efficiency of sunlight depends on how we convert it.
The efficiency of an ideal heat engine, which exceeds the Landsberg limit, was shown by the authors. This is also the case for multicolor radiation.
This helped resolve a problem related to an optical device. An optical diode could increase the temperature of the absorber above the sun temperature by allowing only one-way light propagation. The second law of thermodynamics is violated by this. According to the study, an infinite number of photon recycles would be needed to reach the Carnot efficiency.
The limiting efficiency of a nonreciprocal single-cell photovoltaic conversion was derived from the thermodynamic considerations to nonequilibrium photon distributions.
Sergeev says that the research was motivated by the development of low-cost photovoltaic materials with high quantum efficiency.
The development of high-efficiency photovoltaics may be expected in the near future with the rise of nonreciprocal structures. This study provides hope for solar cell technology as the search for sustainable solutions to the world's energy crisis continues.
More information: Andrei Sergeev et al, Nonreciprocal photonic management for photovoltaic conversion: design and fundamental efficiency limits, Journal of Photonics for Energy (2022). DOI: 10.1117/1.JPE.12.032207 Provided by SPIE--International Society for Optics and Photonics
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