Near-Unity Broadband Photonic Metamaterial Absorber for Thermoelectric Energy Harvesting in Space

Abstract

Spaceborne power systems must operate reliably for decades with minimal maintenance. Thermoelectric generators (TEGs) are intrinsically suited to long-lived missions, but their output remains constrained by available thermal gradients and the limitations of bulk thermoelectric materials. Here, we introduce a photonic metamaterial (PtMM) coating concept that amplifies the thermal gradient available to a TEG by converting incident AM0 solar irradiance into strongly localised photothermal energy on the TEG hot side. We design, optimise, and numerically characterise two metal-insulator-metal PtMM geometries – Nanocross (NC-PtMM) and Nanosquare (NS-PtMM) – using standard thin-film materials. The optimised NC-PtMM achieves near-unity peak absorptance (≈ 99%) and > 95% average absorptance across the visible band, with strong field confinement at the resonator/spacer interface that concentrates dissipated power. Coupled electromagnetic–thermal simulations quantify (i) steady/quasi-steady temperature localisation under continuous irradiation and (ii) the intrinsic non-equilibrium photothermal response under ns-scale pulse trains used as a transient probe. The designs are effectively polarisation-insensitive at normal incidence; NS-PtMM is included as a manufacturability-motivated reference geometry, while detailed NS-PtMM optimisation is left for future work. The material stack (Cr, Al2O3, Al/SiO2, and an optically thick Ag ground plane) is compatible with standard microfabrication routes, and we outline a Space-qualification screening matrix (atomic oxygen exposure, radiation/TID, and thermal-vacuum cycling). Overall, the results establish a practical pathway toward metamaterial-augmented thermoelectric harvesting for compact Space platforms (e.g., CubeSats and landers) and motivate related photothermal coating concepts for spacecraft thermal management and hybrid PV-TEG harvesting.