Thermal stability of tungsten based metamaterial emitter under medium vacuum and inert gas conditions.

Commercial deployment of thermophotovoltaics (TPV) is lacking behind the implementation of solar PV technology due to limited thermal stability of the selective emitter structures. Most of the TPV emitters demonstrated so far are designed to operate under high vacuum conditions (10 mbar vacuum pressure), whereas under medium vacuum conditions (10 mbar vacuum pressure), which are feasible in technical implementations of TPV, these emitters suffer from oxidation due to significant O partial pressure. In this work, the thermal stability of 1D refractory W-HfO based multilayered metamaterial emitter structure is investigated under different vacuum conditions. The impact of the O partial pressure on thermal stability of the emitters is experimentally quantified. We show that, under medium vacuum conditions, i.e. ~10 mbar vacuum pressure, the emitter shows unprecedented thermal stability up to 1300 °C when the residual O in the annealing chamber is minimized by encapsulating the annealing chamber with Ar atmosphere. This study presents a significant step in the experimental implementation of high temperature stable emitters under medium vacuum conditions, and their potential in construction of economically viable TPV systems. The high TPV efficiency, ~50% spectral efficiency for GaSb PV cell at 1300 °C, and high temperature stability make this platform well suited for technical application in next-generation TPV systems.