Thermodynamic performance of near-field electroluminescence and negative electroluminescent refrigeration systems

Abstract

Electroluminescent (EL) and negative electroluminescent (NEL) devices are radiative thermoelectric energy converters that use electric power for refrigeration. For the EL system, we apply a forward bias to the emitter that we want to cool, whereas a reverse bias voltage is applied to the hot absorber for the NEL system. In this work, we derive the thermodynamic limits of the cooling power density and coefficient of performance (COP) of near-field EL and NEL refrigeration systems based on entropy analysis that considers near-field effects. We show numerically that operating the EL and NEL systems in the near-field regime could increase the cooling power density and the COP bounds to a certain extent. As the vacuum gap decrease from 1000 to 10 nm, the near-field effects improve the performance of the NEL system all the time, but the performance of the EL system increases to the optimal value and then decreases. In addition, the increase in temperature difference weakens the performance of both refrigeration systems greatly. Moreover, we also investigate the effects of the absence of sub-bandgap thermal radiation on the performance of the EL and NEL systems. Our work indicates significant opportunities for evaluating the performance of near-field radiative thermoelectric energy converters from the perspective of thermodynamic limits. Meanwhile, these results establish the targets for cooling power density and COP of the near-field EL and NEL systems.