KSEF RDE: Experimental Investigation of Near-Field Radioactive Transfer forHigh-Efficiency Thermophotovoltaic Power Generators

Low-cost efficient clean energy production is one of the most challenging problems of this century. Thermophotovoltaic (TPV) power generation is an attractive way to produce electricity, but due to the current knowledge on radiative heat transfer and photovoltaic (PV) energy conversion, these systems suffer from quite low-efficiencies. TPV devices work in a similar way of solar cells, except that a high temperature radiator is used as emitter of photons. The increase in radiative energy is a key requirement to improve the efficiency of TPV devices; however, theoretically, the radiative transfer rate is limited by the Planck blackbody law. Yet, if the distance between the emitter and the receiver is less than 100 nm, the radiative flux can be enhanced by several orders of magnitude beyond the Planck law. More specifically, higher efficiencies can be achieved by increasing the amount of energy transferred from the emitter toward the absorber, tuning the spectrum of emission of the emitter above the bandgap of the absorber, and/or by tuning the bandgap of the absorber as a function of the emission spectrum of the emitter. Following that, a novel concept for TPV devices has been proposed some time ago where the emitter (radiator) and the absorber (PV cells) are spaced by a gap of about 100 nanometers or less. In this way, thermal radiation exhibits near-field effects leading to a significant increase of the radiative heat flux (above the values predicted by Planck's blackbody distribution) and a quasi-monochromatic radiative transfer if surface polaritons are thermally excited. Design of high-efficiency nanoscafe TPV power generators is possible only by an in-depth experimental study of the near-field effects of thermal radiation, which has not been done so far. Consequently, the specific objective of this proposal is to measure near-field radiative heat transfer between closely spaced bodies (from nanometers to micrometers), and correlate the experimental results with theoretical predictions based on fluctuational electrodynamics. This investigation is needed since no consistent experimental studies have validated the theoretical predictions obtained using fluctuational electrodynamics in a clear and systematic way. Using the outcome of the proposed work, it will be possible to design and built a nanoscale "prototype" TPV power generator system based on reliable data and analyze its real thermodynamic performances. Such analysis has not been done so far due to a lack of information on near-field effects of radiative transfer. This project has therefore major impacts on both fundamentals aspects of thermal radiation (validation of the theoretical paradigms of near-field thermal radiation), and efficient clean energy production via the optimization of TPV power generation.