Abstract
Energy transferred via thermal radiation between two surfaces separated by nanometer distances can be much larger than the blackbody limit. However, realizing a scalable platform that utilizes this near-field energy exchange mechanism to generate electricity remains a challenge. Here, we present a fully integrated, reconfigurable and scalable platform operating in the near-field regime that performs controlled heat extraction and energy recycling. Our platform relies on an integrated nano-electromechanical system that enables precise positioning of a thermal emitter within nanometer distances from a room-temperature germanium photodetector to form a thermo-photovoltaic cell. We demonstrate over an order of magnitude enhancement of power generation (Pgen ~ 1.25 μWcm−2) in our thermo-photovoltaic cell by actively tuning the gap between a hot-emitter (TE ~ 880 K) and the cold photodetector (TD ~ 300 K) from ~ 500 nm down to ~ 100 nm. Our nano-electromechanical system consumes negligible tuning power (Pgen/PNEMS ~ 104) and relies on scalable silicon-based process technologies.
Highlights
Energy transferred via thermal radiation between two surfaces separated by nanometer distances can be much larger than the blackbody limit
At nanometer distances, strong heat exchange occurs due to evanescent modes, thermal radiation that cannot propagate from the hot body towards the far-field, but can evanescently couple from a hot to a cold surface when the separation is sub-wavelength[1,2,3,4,5,6,7,8,9,10,11,12,13]
While the underlying theory of heat exchange via near-field radiation has been widely studied over the past decade, it has only been recently demonstrated for energy generation using a lab-scale table-top experiment based on precision nano-positioning systems[32], or platforms relying on intermediate material spacers that limit the possible near-field enhancement[33]
Summary
Energy transferred via thermal radiation between two surfaces separated by nanometer distances can be much larger than the blackbody limit. Near-field radiative heat exchange have been demonstrated to overcome the blackbody limit at small gaps (d) between the hot and cold surfaces and scales as 1/dα (1 ≤ α ≤ 2; α is a geometrydependent factor) Potential applications of this effect include electricity generation on-demand from heat exchangers and thermal management systems in industrial and space applications[14,15,16,17,18,19,20]. Realizing a scalable platform that utilizes near-field heat transfer to generate electricity remains a challenge due to difficulty of fabricating two large-area surfaces separated by a small gap, while simultaneously maintaining a large temperature differential between the surfaces as required for energy harvesting[21,22,23,24,25,26,27,28,29]. While the underlying theory of heat exchange via near-field radiation has been widely studied over the past decade, it has only been recently demonstrated for energy generation using a lab-scale table-top experiment based on precision nano-positioning systems[32], or platforms relying on intermediate material spacers that limit the possible near-field enhancement[33]
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