A novel selective thermophotovoltaic emitter based on multipole resonances

Thermophotovoltaic systems can harvest electric energy from heat sources with a potential efficiency exceeding the Shockley-Queisser limit due to the selective emission of an elaborate thermal emitter. In this work, a two-dimensional nanodisks/thin-film metamaterial is proposed as a wavelength-selective emitter, which can coordinate well with the photovoltaic cell in a thermophotovoltaic system. Compared to conventional emitters based on surface plasmon polaritons, the emittance peaks of the proposed emitter are realized by the excitations of both electric dipole and anapole modes in silicon nanodisks, which can be easily tailored due to the non-dispersive optical constants of dielectric materials. Meanwhile, the effect of polarization and polar angle on the emittance spectra is also investigated, suggesting that the proposed emitter has high emittance and efficiency not only in the normal direction but also at large oblique angles. Electromagnetic field and current density distributions reveal that the coupling between multipole resonances and the bottom tungsten layer can induce a magnetic dipolar resonance. Therefore, the wavelengths of both emittance peaks are sensitive to the period paralleled to the incident electric field. Besides, the anapole-induced mode can couple with the lattice resonance, resulting in higher emittance. Moreover, the proposed emitter is successfully fabricated, and the measured spectra agree well with the theoretical results. The fundamental understanding and insights obtained here will facilitate the active design and application of novel multipole-based emitters in enhancing energy conversion. (c) 2021 Elsevier Ltd. All rights reserved.

Automated summary

Thermophotovoltaic systems can increase energy conversion efficiency by utilizing a two-dimensional nanodisks/thin-film metamaterial as a wavelength-selective emitter. The proposed emitter achieves high emittance peaks through electric dipole and anapole modes in silicon nanodisks, and can be tailored easily due to non-dispersive optical constants. Additionally, the coupling between multipole resonances and the bottom tungsten layer induces a magnetic dipolar resonance, leading to sensitive wavelengths and higher emittance.