Tungsten nanodisc-based spectrally-selective polarization-independent thermal emitters
Thermophotovoltaic (TPV) cells convert thermally emitted photons into electrical power using photovoltaic (PV) detectors. To realize highly efficient thermal energy harvesting using TPV conversion, high-temperature stable spectrally-selective emitters are needed. The deployment of TPV technology lags behind conventional solar-PV technology due to the lack of large-scale fabrication of efficient thermal emitters, which would preferentially emit in the PV cell absorption band. In this work, we demonstrate a simple large-area nanofabrication method based on the hole-mask colloidal lithography and sputtering, which allows one to fabricate tungsten (W) nanodisc spectrally-selective emitters (consisting of a metal-insulator-metal configuration) with a high emissivity below the InGaAsSb PV-cell cut-off wavelength of 2.25 μm and a gradually decreasing emissivity (down to < 10%) in the mid-infrared region. Frequency-domain time-domain (FDTD) simulations reveal that the spectral selectivity is achieved due to the localized surface plasmon resonance of W nanodiscs strongly influenced by the insulator thickness. Importantly, the W emitters show thermal stability at temperatures of up to 1100 °C, and emissivity invariance to changes in polarization and incidence angles up to 65°. This work represents a significant step towards the realization of high-temperature stable efficient thermal emitters by a facile and cost-effective fabrication method, thereby promoting the implementation of photonic/plasmonic thermal emitters in the next-generation thermal energy harvesting systems. The method proposed in this study holds potential for scalability; however, empirical evidence to demonstrate this scalability has not yet been established. Subsequent studies are needed to confirm the scalability of the proposed method and its extensive applicability.