Performance analysis of thermophotovoltaic system with an equivalent cut-off blackbody emitter

Abstract

The general thermophotovoltaic (TPV) system can get high efficiency, by adding a spectral filter or using a selective thermal emitter, but the output power density is very low. However, the microgap TPV system can get high output power density, but the efficiency is relatively low, due to the difficulty of cropping the emissive spectrum of the thermal emitter in the near field. Thus, the ultimate goal of designing a TPV system is to get higher efficiency and higher output power density, simultaneously. Theoretically, the way used in this paper is to place a perfect edge reflector at the back of the PV diode to achieve an equivalent cut-off blackbody emitter. The performance of this ideal TPV system is calculated based on a fluctuational electrodynamics model. According to the simulation results, in the far field, the performance of this ideal TPV system is identical to the well known thermodynamic limit. In the near field, this ideal TPV system can simultaneously get higher efficiency and higher output power density. By assuming the emitter with a frequency-independent permittivity, a permittivity-match emitter is proposed to maximize the output power density, there is an optimal vacuum distance between 110 and 160 nm to maximize the efficiency, and near-field effect disappears for TPV system with a zero-refractivity emitter.