Theoretical study of multilayer ring metamaterial emitter for a low bandgap TPV cell

•A multilayer nano-ring metamaterial emitter was designed to improve the radiation performance.•The multilayer ring emitter exhibited broadband, angle-insensitive and polarization-independent emission.•The mechanism of the emittance enhancement was revealed through the distributions of the Poynting vector.•The multilayer ring emitter demonstrated a spectral efficiency (ηSP) of 85.6% at 1600 K for InGaAsSb. To improve the conversion efficiency of InGaAsSb, we designed a multi-layer ring metamaterial (MTM) emitter with a cut-off wavelength of 2.34 µm based on theoretical calculation. By adjusting the geometric parameters, such as the width of the periodic structure, the number of layers, the radii and thickness of the multilayer rings, and the thickness of the dielectric substrate, an optimal structure that matched the external quantum efficiency of the InGaAsSb cell was obtained. Through numerical simulation, the emitter demonstrated a mean emittance of 0.91 in the wavelength range of 0.5–2.4 µm. Additionally, our emitter can obtain a spectral efficiency of 85.6% for the InGaAsSb cell at 1600 K, thereby significantly improving the efficiency of the TPV.