NOVELTY - A thermoelectric device comprises a thermoelectric material layer comprising a thermoelectric material; a transition layer (2) on the thermoelectric material; and a diffusion prevention layer (3) on the transition layer.    USE - As thermoelectric device used in thermoelectric module for thermoelectric apparatus comprising power-generation apparatus (claimed).    ADVANTAGE - The thermoelectric device has low interfacial resistance and a high mechanical strength, thus improves efficiency of power-generation apparatus; and has improved thermal and mechanical stability.    DETAILED DESCRIPTION - A thermoelectric device comprises a thermoelectric material layer comprising a thermoelectric material; a transition layer (2) on the thermoelectric material; and a diffusion prevention layer (3) on the transition layer, where the thermoelectric material comprises a compound of formula (A1-aA'a)4-x(B''1-bB'b)3-y-zC'z (I) where A and A' are different from each other, A is a Group 13 element, and A' is at least one element of a Group 13 element, a Group 14 element, a rare-earth element, or a transition metal, B and B' are different from each other, B'' is a Group 16 element, and B' is at least one element of a Group 14 element, a Group 15 element, or a Group 16 element, C' is at least one halogen atom, a is 0.1-1, b is 0.1-1, x is -1 to 1, y is -1 to 1, and z is 0.1 to 0.5. INDEPENDENT CLAIMS are included for the following:    (1) a thermoelectric module comprising an n-type thermoelectric device and a p-type thermoelectric device; and top and bottom electrodes to which the p-type thermoelectric device and the n-type thermoelectric device are attached so that the p-type thermoelectric device and the n-type thermoelectric device are alternately arranged, where each of the n-type thermoelectric device and the p-type thermoelectric device comprise a thermoelectric material layer comprising a thermoelectric material, a transition layer, and a diffusion prevention layer;    (2) a thermoelectric apparatus comprising the thermoelectric module and optionally a heat supplier; and    (3) manufacturing a thermoelectric device, involving disposing a top portion of a diffusion prevention layer powder, a top portion of a transition layer powder, a thermoelectric material powder, a bottom portion of the transition layer powder, and bottom portion of the diffusion prevention layer powder sequentially and in the foregoing order in a mold; compression-molding to form a powder body; vacuum hot-pressing the powder body by heating and compressing the powder body in a vacuum to form a compression-molded body; and rapidly cooling the compression-molded body to manufacture the thermoelectric device, where the thermoelectric device comprises a diffusion prevention layer integrally attached to top and bottom portions of the thermoelectric device.    DESCRIPTION OF DRAWING(S) - The figure shows cross-sectional view of thermoelectric module.    Transition layer (2)    Diffusion prevention layer (3)    Contact layer (4)    Adhesive layer (5)    Electrode (6)