Integrated Near-Field Thermophotovoltaic Device Overcoming Blackbody Limit

Abstract

Near-field thermal radiation transfer overcoming the far-field blackbody limit has attracted significant attention in recent years owing to its potential for drastically increasing the output power and conversion efficiency of thermophotovoltaic (TPV) power generation systems. Here, we experimentally demonstrate a one-chip near-field TPV device overcoming the far-field blackbody limit, which integrates a 20-µm-thick Si emitter and an InGaAs PV cell with a subwavelength gap (<140 nm). The device exhibits a photocurrent density of 1.49 A/cm 2 at 1192 K, which is 1.5 times larger than the far-field limit at the same temperature. In addition, we obtain an output power of 1.92 mW and a system efficiency of 0.7% for a 1-mm 2 device, both of which are one to two orders of magnitude greater than those of the previously reported nearfield systems. Detailed comparisons between the simulations and experiments reveal the possibility of a system efficiency of >35% in the up-scaled device, thus demonstrating the potential of our integrated near-field TPV device for practical use in the future.

Thermophotovoltaic Energy Conversion in Far-to-Near-Field Transition Regime

“…These conditions make maintaining the nanoscale vacuum gap quite challenging because of structural deformation by thermal stress. 41 Recently, Inoue et al 13 have developed a one-chip NF-TPV device working with an area of 1 mm 2 , a vacuum gap <140 nm, and a temperature difference of ∼900 K. They discussed that an up-scaled device is required to further improve the system efficiency by reducing the conduction and thermal radiation losses. However, it would be challenging to maintain high power density for up-scaled NF-TPV devices because of the inevitable series resistance losses primarily caused by the large photocurrent.…”

“…Since the concept of the NF-TPV device was proposed by Whale and Cravalho, there have been only a few groups who have experimentally realized NF-TPV devices, ,,− despite the substantial progress in measuring the near-field radiation. ,− ,− The main factors of experimental difficulty are the essential requirements for a practical high-power-output NF-TPV device: a large heat transfer area and a large temperature difference between the emitter and the PV cell. These conditions make maintaining the nanoscale vacuum gap quite challenging because of structural deformation by thermal stress .…”

“…While the spectral measurement of near-field radiation has been considered unfeasible, the PV cell offers a direct way to measure narrow-band radiative heat flux. Even for the case in which the emitter supports the surface mode (i.e., the radiation penetration depth will be shorter compared to the case that only the frustrated mode is supported), this idea will be available for introducing thin-film PV cells that can show near-100% internal quantum efficiency. ,, If the band-gap energy of the PV cell can be well controlled by changing the alloy composition in III–V ternary or quaternary compound semiconductors or the temperature of the PV cell, it will be possible to measure the spectral near-field radiation in the particular infrared region.…”

“…Accordingly, most studies on NF-TPV experiments − have taken extensive measures to reduce the vacuum gap between the emitter and the PV cell because the radiative heat flux by evanescent waves increases as the gap decreases. However, unlike the near-field radiative heat transfer, which takes advantage of the full spectral range, the PV cell can generate electrical energy exclusively from photons, whose energy is greater than the band gap.…”

Optical axis-driven modulation of near-field radiative heat transfer between two calcite parallel structures

“…Moreover, it has been demonstrated that the NFRHT has broad prospects in thermal energy harvesting, 12 thermal transistors, 13 and near-field thermophotovoltaics. [14][15][16][17] Therefore, it is of great importance to investigate the NFRHT.…”