QED provides the world record 100 % conversion of heat to electricity

YOUNGWOOD, Pa. - June 7, 2014 - PRLog -- .
Background
Solar energy conversion based on a TPV cell converts heat to electricity by photons. TPV stands for thermophotovoltaic. Indeed, solar TPV cells have an inherent limit on the efficiency at which they can convert sunlight into energy. The Shockley-Queisser limit is about 33.7 % because of the inability of any solar cell to respond to all wavelengths of sunlight. Typically, the hot TPV temperature varies from 900 to 2000 C, the BB radiation of which is mostly in the near IR.  TPV cells can absorb some of the BB photons and convert them into electrical current, but the efficiency is low as the frequency of the TPV cell simply cannot be matched to that of the entire BB spectrum.

By taking advantage of filters, the BB emissions in a narrow wavelength range can be modified to a frequency that is optimal for the TPV cell. It is thought TPVs can make more efficient use of the entire solar spectrum by selective filtering of the BB spectrum. For BB photons with energy E^b < the bandgap E^g of the TPV cell cannot generate electron-hole pairs, and are dissipated by generating heat. Conversely, BB photons having energy E^b > the bandgap E^g can be absorbed, but the excess energy, E^b - E^g is lost by heat dissipation. Since the BB spectrum is broadband, it is highly unlikely the entire BB spectrum can ever be converted to the frequency of the bandgap E^g to achieve the much sought after 100 % efficiency.

TPV cells having 100 % efficiency require all BB photons be converted to electricity. In addition to selective emission, photon recycling is thought to enhance efficiency. By placing reflectors behind the TPV cell, BB photons are directed back to the emitter, where they can be reabsorbed to generate heat and create additional BB photons. An idealized TPV system would use photon recycling and selective emission to convert all BB photons into electricity.

Recently, a new world record of 44.7 % was claimed [1] for the conversion of sunlight into electricity using a new TPV solar cell structure with four solar sub-cells. Although < 100% efficient, the world record is significant, but still indicates that only 44.7% of the solar spectrum's energy, from UV through to the IR is converted into electrical energy. See http://www.soitec.com/en/news/press-releases/world-record-solar-cell-1373/

Problem

TPV solar cells that convert heat to light have been based on classical physics that implicitly assumes the efficiency of the solar cell is independent of the thickness of the thin films that comprise the cells. i.e., all atoms in thin films have heat capacity. Only time will tell if TPV cell solar efficiency of 100 % efficiency is consistent with this approach.

In the alternative, QM differs by requiring the heat capacity of the atom to vanish in thin films, the consequence of which is expected to make a significant difference in achieving 100% TPV cell efficiency. QM stands for quantum mechanics. What this means is BB radiation supplied to a thin film does not increase the temperature of the film, but rather is induced by QED to create EM radiation that charges the film or is lost to the surroundings. QED stands for quantum electrodynamics, and EM for electromagnetic. See http://www.nanoqed.org  , at  2010-2014.

QED Configuration for a TPV

The QED induced TPV cell resting on a hot 1200 C surface of a combustion process is illustrated in the thumbnail. The hot surface emits BB radiation photons shown in red that  are absorbed in a the TPV cell which is, say a single ultrathin 50 nm aluminum  film. Aluminum like most metals has a high quantum yield of electrons/QED photon while having high IR absorption of BB photons. However, BB photons absorbed in the aluminum film do not increase its temperature. Instead, QED creates EM radiation that charges the film. But the quantum yield of  electrons / QED photon is 0.01 to 0.1 < 1 so not all QED photons create electrons. Some QED radiation shown in green is returned to the hot source or lost to the upper housing.  The lost QED radiation may be minimized by providing a series of TPV cells, but for clarity only a single TPV cell is shown.

QED Theory

The TPV cell comprises an ultrathin aluminum film interposed between the hot source and the housing, The RI of the aluminum film need only be greater than that of the surroundings. RI stands for refractive index.

Under these conditions, any BB radiation absorbed by the film is placed under TIR confinement, the importance of which is the QED radiation created has sufficient Planck energy to ionize the aluminum film. TIR stands for total internal reflection. Here, the QED wavelength λ = 2nd, where n and d are the refractive index and thickness of the film. For Planck's constant h and the velocity of light c, the Planck energy E of the QED radiation is beyond the UV, E = hc / λ > 5 eV.

The QED effect in TPV cells is not new. Indeed, the literature [2] shows the QED effect in producing the voltage across a pair of thin 200 nm Samarium-Sulfide films heated to about 428K. Of note, the Seebeck effect that depends on the voltage  proportional to the temperature gradient was shown not to be operational. More recently, the QED effect as proposed [3] based on one of Tesla's patents.


Conclusions

Unlike the Seebeck effect,the QED effect in ultrathin metallic films does not depend on temperature gradients. The TPV cell produces voltage because QM precludes the atoms in ultrathin films from having the heat capacity to increase in temperature upon absorbing BB radiation from the hot surface of a combustion device. Instead, the BB radiation is conserved by creating QED induced EM radiation within the film thereby producing the charge allowing the TPV cell to function as a battery.

The QED effect always produces charge in nanostructures that may be used as a battery, the efficiency of which does not depend on the frequency of the BB photons. Whether or not the frequency of the BB photon matches that of the TPV cell .is irrelevant as heat dissipation precluded by QM is converted to charge by QED. What this means is 100 % efficient TPV cells based on QED may be expected in the future. TPV cells based on matching the frequency of BB photons are not likely to be competitive.

References

[1] E. Yablonovitch, “Regenerative Thermo-PhotoVoltaics, a New Opportunity in Radiative Science,” IAS – HKUST , May 28, 2014. http://ias.ust.hk/web/ias/eng/event_detail.php?p=&tid...
[2] V. V. Kaminski and M. M. Kazanin, “Thermovoltaic Effect in Thin-Film Samarium-Sulfide-Based Structures,”Technical Physics Letters, V. 34, pp. 361–362, 2008.
[3] T. Prevenslik, "Quantum Mechanics In Submicron Thin Metal Films Allows Full Solar Spectrum Conversion To Electricity," Feb. 3, 2010. See www prlog.org/10516499-quantum-mechanics-in-submicron-thin-metal-films-allows-full-solar-spectrum-conversion-to-electricity.html