Three-dimensional metallo-dielectric selective thermal emitters with high-temperature stability for thermophotovoltaic applications

Abstract

Selective thermal emitters concentrate most of their spontaneous emission in a spectral band much narrower than a blackbody. When used in a thermophovoltaic energy conversion system, they become key elements defining both its overall system efficiency and output power. Selective emitters' radiation spectra must be designed to match their accompanying photocell's band gap and, simultaneously, withstand high temperatures (above 1000 K) for long operation times. The advent of nanophotonics has allowed the engineering of very selective emitters and absorbers; however, thermal stability remains a challenge since 1 of 22 nanostructures become unstable at temperatures much below the melting point of the used materials. In this paper we explore an hybrid 3D dielectric-metallic structure that combines the higher thermal stability of a monocrystalline 3D Silicon scaffold with the optical properties of a thin Platinum film conformally deposited on top. We show experimentally that these structures exhibit a selective emission spectrum suitable for TPV applications and that they are thermally stable at temperatures up to 1100 K. These structures are ideal in combination with III-V semiconductors in the range Eg=0.4-0.55 eV such as InGaAsSb (Eg=0.5-0.6 eV) and InAsSbP (Eg=0.3-0.55 eV).

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“…It may be achieved by using cold-side filters [67], modifying the photonic density of states to achieve wavelength selectivity, or combining emitter selectivity with a filter [29]. The 1D, 2D or 3D PhCs [50,61,[68][69][70] and metamaterials [52,54,71] are good examples of structures that can strongly modify the photonic density of states. In fact, among all of these approaches, 2D metallic PhCs have garnered the greatest interest for STPV systems [6,7,68], because of the high abundance ranking of refractory metals, and the ability to preferentially tailor near-blackbody emissivity at the designed wavelength range and suppress emission outside.…”

“…Also, Kohiyama et al proposed a closed-end surface microcavity array to improve the emission quality factor and hence suppress thermalization losses [75]. Three-dimensional PhCs are also proposed as efficient thermal emitters, either being an allmetallic structure, as first proposed in [61,76], or with a metal-coated silicon or carbon scaffold for improved thermal stability [70,77]. Figure 8E (inset) shows an example of a 3D metallo-dielectric structure and the measured selective emission at 889 K is shown in Figure 8E.…”

“…(D) A polar plot of the average emittance below the cutoff wavelength (i.e., λ 2 µm) for W PhC design II [55]. (E) (inset) Scanning electron microscope image of the broken side of a 3D Si/Pt PhC [70]. The ALD Pt film covers the full 3D structure.…”

“…(right) Normalized radiant intensity polar plot for several wavelengths. The dashed line represents the blackbody curve [70]. (F) Designed metamaterial with wide-band emissivity from [71] (blue curve) and EQE (red curve) of GaSb.…”

“…Experiments have shown that nano-and microstructures degrade under high temperature exposure for long times [148][149][150][151]. Different mechanisms can lead to such degradation, including chemical reactions [33,70,150], recrystallization [34,148] and surface diffusion [152,153]. These structural degradation processes could eventually remove the fine features of the structure.…”