Effect of interface layer on the cooling performance of a single thermoelement

The resultant thermoelectric (TE) figure of merit Z, the coefficient of performance (COP), the heat pumping capacity per unit area (Q_c/S) were derived analytically as functions of l₀, ρ_c, κ_c and s_c for a single thermoelement (STE) by taking into account the interface layers, where l₀ is a length of a TE material, ρ_c the electrical interface resistivity, κ_c the thermal interface conductivity and s_c the ratio of the Seebeck coefficient of an interface layer to that of a TE material. As a result, it was first revealed that the increase in Z₀T of a TE material is not necessarily reflected in the increase in ZT of an STE as long as the interface layers are present. The COP and Q_c/S are lowered remarkably for s_c = 0 and κ_c ? 10⁴ W/m² K. However, it was clarified that even for low values of κ_c, the COP and Q_c/S return to the original high values (obtained for κ_c ? 10⁵ W/m² K) at s_c = 0.45 and 0.90, respectively. The definite criterion of s_c whether or not the boundary Seebeck coefficient has an effect on the enhancement of the cooling performance was indicated quantitatively for an STE with interface layers.