High-temperature differences in plasmonic broadband absorber on PET and Si substrates

The characteristics of a plasmonic resonator with a metal-dielectric-metal structure is influenced by the size, shape, and spacing of the nanostructure. The plasmonic resonators can be used in various applications such as color filters, light emitting diodes, photodetectors, and broadband absorbers. In particular, broadband absorbers are widely used in thermophotovoltaics and thermoelectrics. To achieve a higher photothermal conversion efficiency, it is important to provoke a larger temperature difference in the absorber. The absorption and thermal conductance of the absorber has a great impact on the temperature difference, but in order to further improve the temperature difference of the absorber, the thermal conductivity of the substrate should be considered carefully. In this study, we designed Cr/SiO₂/Cr absorbers on different substrates, i.e., polyethylene terephthalate (PET) and silicon. Although their optical properties do not change significantly, the temperature difference of the absorber on the PET substrate is considerably higher than that on the Si substrate under laser illumination, i.e., 164 K for ΔT_PET and 3.7 K for ΔT_Si, respectively. This is attributed to the thermal conductance of the substrate materials, which is confirmed by the thermal relaxation time. Moreover, the Seebeck coefficient of graphene on the absorber, 9.8 μV/K, is obtained by photothermoelectrics. The proposed Cr/SiO₂/Cr structure provides a clear scheme to achieve high performance in photothermoelectric devices.