  Metasurfaces are artificial thin materials that achieve optical thickness
through thin geometrical structure. This feature of metasurfaces results in
unprecedented benefits for enhancing the performance of optoelectronic devices.
In this study, we report that this metasurface feature is also essential to
drive photo-thermoelectric conversion, which requires the accumulation of
thermal energy and effective heat conduction. For example, a
metasurface-attached thermoelectric device placed in an environment with
uniform thermal radiation generates an output voltage by gathering the thermal
energies existing in the environment and creating an additional thermal
gradient across the thermoelectric element. In contrast, when a
100-um-thick-carbon-black-coated electrode was used instead of the metasurface,
the device showed low-er thermoelectric performance than that of the
metasurface-attached device although carbon black exhibits higher infrared
absorption than the metasurface. These results indicate that metasurface
characteristics of optical thickness and thin geometrical structure for
achieving the high thermal conductance are essential in enhancing the
performance of photo-thermoelectric devices in terms of the effective
collection of thermal energies and conduction of local heating.
