Optical metamaterials refer to artificial structures with exotic optical properties that cannot be obtained in naturally occurring materials [5]. Selective absorption has been investigated in metamaterials made of different micro/nanostructures from GHz to IR spectral regime, including split-ring-resonators [6] and [7], fishnet [8], cut-wires [9] and [10] and photonic crystals [11]. Recently, film-coupled metamaterials in metal–insulator–metal configurations have been intensively studied as thermal emitters or selective absorbers from visible to NIR spectral regime. Wang and Zhang designed a diffuse-like spectrally-selective thermophotovoltaic (TPV) emitter with 1D tungsten gratings on top of a SiO2 spacer and tungsten substrate [12], while Zhao et al. modeled the polarization-independent 2D counterparts [13]. Note that selective TPV emitters can also be used as selective solar absorbers due to their spectral selectivity being well-matched to the solar spectrum. Photonic crystals [14] and [15] and nanoparticles [16], [17] and [18] were also proposed for selective absorption in the visible and NIR range. Highly efficient solar absorbers require a broad absorption band from visible to NIR range, which could be possibly attained with lossy materials and geometric approaches. Wang and Wang proposed selective metamaterial solar absorbers with multi-sized tungsten patch arrays [19]. Aydin et al. discussed an ultra-thin broadband selective absorber composed of trapezoid gratings [20]. In addition, Lee et al. numerically explored a film-coupled nickel concave grating as a selective absorber for solar thermal energy harvesting [21].