Thermodynamic bounds of work and efficiency in near-field thermoradiative systems

Abstract Thermoradiative (TR) device combined with near-field radiation has been recently proposed to enhance noncontact direct photoelectric energy conversion. Based on the fluctuation-dissipation theorem, we evaluate the maximum work flux and the fundamental efficiency limit of the near-field TR systems by analyzing the radiative heat flux and the entropy flux. For a near-field TR system, when the ZrC absorber is placed close to the TR cell with a vacuum gap down to 100 nm, photon tunneling through evanescent waves can significantly enhance the maximum work flux without a compromise in efficiency limit. Furthermore, the decrease in the temperature of the heat source would greatly weaken the performance of the TR system. We also would like to emphasize that the hyperbolic metamaterial (HMM) and Lorentz absorbers can remarkably improve the performance of the TR system as compared to the ZrC reference. In this paper, based on the proposed method for determining the thermodynamic bounds of work and efficiency, we establish a target for the performance of the near-field TR system. In addition, the fundamental understandings and insights obtained in this study will facilitate the design and application of the near-field TR system.