Near-field thermal radiative energy conversion devices

Abstract

This study aims to establish a performance analysis model of near-field thermal radiative energy conversion devices and experimentally validate the performance enhancement for the near-field thermophotovoltaic (NFTPV) system. It has been shown that the performance of a thermal radiative energy conversion device, such as thermophotovoltaic (TPV) and electroluminescent (EL) refrigerator, can be significantly enhanced when a gap between a thermal reservoir and a semiconductor diode becomes nanoscale. As theoretical works on the NFTPV system, we cover a Schottky TPV system that uses metal-semiconductor junction photodiode and a tandem TPV system using a multi-junction cell in which two p-n junction diodes are monolithic interconnected. The performance simulation model of each system is developed considering the movement of carriers inside the TPV cell. Further, we study a TPV-LED integrated near-field EL refrigeration system consisting of two graphene-semiconductor Schottky photodiodes. The performance of the integrated near-field refrigeration system is analyzed based on the radiative detailed balance relation. The cooling performance of the system could be improved by recycling the electric power generated in the TPV cell. For experimental work on near-field thermal radiation, we designed and manufactured MEMS-fabricated microdevices involving heat flux and vacuum gap distance sensors. We demonstrate substantially increased near-field radiative heat transfer between asymmetric planar structures by employing a thin-Ti-film plasmonic coupler. Finally, using an Au/n-GaSb Schottky-junction-based photovoltaic cell manufactured by the MEMS fabrication process, we experimentally validate the performance enhancement of the sub-micron-gap NFTPV system at a far-to-near-field coherent regime.