Lattice defects and thermoelectric properties: the case of p-type CuInTe2 chalcopyrite on introduction of zinc

Abstract

I–III–VI₂ chalcopyrites have unique inherent crystal structure defects, and hence are potential candidates for thermoelectric materials. Here, we identified mixed polyanionic/polycationic site defects (Zn_In⁻, V_Cu⁻, In_Cu²⁺ and/or Zn_Cu⁺) upon Zn substitution for either Cu or In or both in CuInTe₂, with the Zn_In⁻ species originating from the preference of Zn for the cation 4b site. Because of the mutual reactions among these charged defects, Zn substitution in CuInTe₂ alters the basic conducting mechanism, and simultaneously changes the lattice structure. The alteration of the lattice structure can be embodied in an increased anion position displacement (u) or a reduced bond length difference (Δd) between d_(Cu–Te)4a and d_(In–Te)4b with increasing Zn content. Because of this, the lattice distortion is diminished and the lattice thermal conductivity (κ_L) is enhanced. The material with simultaneous Zn substitution for both Cu and In had a low κ_L, thereby we attained the highest ZT value of 0.69 at 737 K, which is 1.65 times that of Zn-free CuInTe₂.