Iridium Based Selective Emitters for Thermophotovoltaic Applications.

The long-term operation of refractory-metal-based metamaterials is crucial for applications such as thermophotovoltaics. The metamaterials based on refractory metals like W, Mo, Ta, Nb and Re fail primarily by oxidation. Here  we propose the use of the noble metal Ir as an alternative to refractory metals, stable to oxidation and having optical properties comparable to gold.  We demonstrate the thermal endurance of Ir in a 3-layer-system, consisting of HfO 2 /Ir/HfO 2 , by performing annealing experiments up to 1240°C in a pressure range from 2 × 10 -6  mbar to 1 bar. The Ir layer shows no oxidation in vacuum and inert gas atmosphere. At temperatures above 1100°C, the Ir layer starts to agglomerate due to the degradation of the confining HfO 2 layers. Alternative dielectric layers are required to further increase the application temperature. An in-situ x-ray diffraction experimental comparison between 1D multilayered Ir/HfO 2 and W/HfO 2 selective emitters annealed at 1000°C, 2 × 10 -6  mbar over 100 h confirms oxidation stability of Ir while W multilayers gradually disappear. The results of this work show that metamaterials based on oxidizing refractory metals, such as tungsten, are not long-term stable even at 1000°C. The oxidation resistance of Ir can be leveraged for refractory plasmonic metamaterials, such as selective emitters in thermophotovoltaic systems with strong suppression of long wavelength radiation. This article is protected by copyright. All rights reserved.