Near-field radiative heat transfer enhancement in the thermophotovoltaic system using hyperbolic waveguides

As an energy conversion system, the near-field thermophotovoltaic (NTPV) device has attracted much attention. To improve the NTPV system output power, an intermediate modulator with the same plasmonic properties as thermal emitters can be intercalated into the two-body system. Surface modes are coupled in the vacuum gap between the modulator and the emitter. The modulator absorbs the enormous radiative energy produced by the coupling of surface modes and transfers it to the cell. However, due to the low penetration depth of surface modes and the loss of energy transmission in the intermediate slab, the direct heat exchange between the emitter and the cell in the three-body system is much smaller than that in the corresponding two-body system. In the present study, we design a hyperbolic metamaterial (HMM)-based three-body NTPV system. Ga-doped ZnO (GZO)/HfO2-multilayer-based HMMs serve as the emitter and the modulator, and GaSb works as the cell. The radiative heat flux from the emitter to the cell is enhanced by the weakly dissipating hyperbolic waveguide, which is attributed to the coupling of the vacuum-GZO surface plasmon polariton (SPP) and the SPPs at the GZOHfO2 interfaces in the HMM modulator. Compared with the GZO slab emitter, the HMM emitter emits higher spectral heat flux located in the hyperbolic region. Different top layers of the HMM affect the coupling of surface modes. These findings provide a new way to enhance the three-body NTPV system output power.