“…[17][18][19][20][21] The experimentally reported TR of thermal rectification devices, applicable for a wide range of temperatures, was relatively low. 4,6,7,[9][10][11][14][15][16] Thermal radiation is a promising rectification mechanism due to the strong non-linear dependence of radiation heat transfer rate (Q rad ) on temperature (T) and its unbound operating temperature range. 7 The non-linearity is described by the Stefan-Boltzmann law, Q rad = etAT 4 , where e is the emissivity, t is the Stefan-Boltzmann constant, and A is the surface area.…”