Nanogap near-field thermophotovoltaics

Abstract

Conversion of heat to electricity via solid-state devices is of great interest and has led to intense research of thermoelectric materials1,2. Alternative approaches for solid-state heat-to-electricity conversion include thermophotovoltaic (TPV) systems where photons from a hot emitter traverse a vacuum gap and are absorbed by a photovoltaic (PV) cell to generate electrical power. In principle, such systems may also achieve higher efficiencies and offer more versatility in use. However, the typical temperature of the hot emitter remains too low (<1,000 K) to achieve a sufficient photon flux to the PV cell, limiting practical applications. Theoretical proposals3,4,5,6,7,8,9,10,11,12 suggest that near-field (NF) effects13,14,15,16,17,18 that arise in nanoscale gaps may be leveraged to increase the photon flux to the PV cell and significantly enhance the power output. Here, we describe functional NFTPV devices consisting of a microfabricated system and a custom-built nanopositioner and demonstrate an ~40-fold enhancement in the power output at nominally 60 nm gaps relative to the far field. We systematically characterize this enhancement over a range of gap sizes and emitter temperatures, and for PV cells with two different bandgap energies. We anticipate that this technology, once optimized, will be viable for waste heat recovery applications.

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Fig. 1: Microscale devices for demonstration of near-field thermophotovoltaic energy conversion.
Fig. 2: Thermophotovoltaic measurement procedure.
Fig. 3: Thermophotovoltaic performance enhancement in the near field.
Fig. 4: Near-field thermophotovoltaic measurement with 0.303-eV-bandgap cell.

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Acknowledgements

P.R. and E.M. acknowledge support from the Army Research Office under awards W911NF-16-1-0195 and W911NF-18-1-0004 (nanopositing and instrumentation), from the Department of Energy-Basic Energy Science under award DE-SC0004871 (scanning probes and experimental design) and the National Science Foundation under award CBET 1509691 (computational modelling). We acknowledge the Lurie Nanofabrication Facility for facilitating the fabrication of devices.

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P.R. and E.M. conceived and supervised the work. A.F. and L.Z. performed the experiments and calculations, and D.T. and R.M. fabricated the emitter devices. The manuscript was written by A.F., P.R. and E.M. with comments and input from all authors.

Corresponding authors

Correspondence to Pramod Reddy or Edgar Meyhofer.

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The authors declare no competing interests.

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Fiorino, A., Zhu, L., Thompson, D. et al. Nanogap near-field thermophotovoltaics. Nature Nanotech 13, 806–811 (2018). https://doi.org/10.1038/s41565-018-0172-5

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