Low-grade waste heat contains an enormous amount of exergy that can be recovered for renewable-energy generation. Current solid-state techniques for recovering low-grade waste heat, such as thermoelectric generators and thermophotovoltaics, however, are limited by low conversion efficiencies or power densities. In this work, we propose a solid-state near-field thermophotonic system. The system consists of a light-emitting diode (LED) on the hot side and a photovoltaic (PV) cell on the cold side. Part of the generated power by the PV cell is used to positively bias the LED. When operating in the near-field regime, the system can have power density and conversion efficiency significantly exceeding the performance of current solid-state approaches for low-grade waste-heat recovery. For example, when the gap spacing is 10 nm and the hot side and cold side are, respectively, 600 and 300 K, we show that the generated electric power density and thermal-to-electrical conversion efficiency can reach 9.6 W/cm² and 9.8%, respectively, significantly outperforming the current record-setting thermoelectric generators. We identify the alignment of the band gaps of the LED and the PV cell, the appropriate choice of thickness of the LED and PV cell to mitigate the effect of non-radiative recombination, and the use of highly reflective back mirrors as key factors that affect the performance of the system. Our work points to the significant potential of photonic systems for the recovery of low-grade waste heat.

中文翻译：

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用于低等级废热回收的近场热光子系统

低品位废热包含大量的本能，可以将其回收以产生可再生能源。然而，目前用于回收低级废热的固态技术，例如热电发电机和热光电技术，受到转换效率或功率密度低的限制。在这项工作中，我们提出了一种固态近场热光子系统。该系统由热侧的发光二极管（LED）和冷侧的光伏（PV）电池组成。PV电池产生的部分功率用于对LED施加正偏压。当在近场状态下运行时，该系统的功率密度和转换效率可以大大超过当前用于低等级废热回收的固态方法的性能。例如，分别为²％和9.8％，大大超过了目前创纪录的热电发电机。我们确定了LED的带隙的取向和PV电池，LED和PV电池的厚度的合适的选择，以减轻非辐射复合的效果，以及使用高反射回反射镜的作为影响的关键因素系统的性能。我们的工作指出了光子系统在回收低级废热方面的巨大潜力。