Towards a new chalcopyrite high-performance thermoelectric semiconductor Cu3InSnSe5 by entropy engineering

A new semiconductor Cu ₃InSnSe ₅ is introduced by entropy driven alloying equimolar ratio CuInSe ₂ and Cu ₂SnSe ₃. Cu ₃InSnSe ₅ is a p-type semiconductor (Eg ∼0.41 eV) and crystallizes in the chalcopyrite structure with I4_2 m space group. Our density functional theory calculations show that Cu ₃InSnSe ₅ exhibits an electronic band structure with multiple valance band peaks, rendering a large density of state effective mass m* of 1.8 m _e. Therefore, Cu ₃InSnSe ₅ has a high power factor of 7.59 μW cm ⁻¹ K ⁻² at 773 K. In addition, Cu ₃InSnSe ₅ also has a low lattice thermal conductivity (0.34 W m ⁻¹ K ⁻¹ at 773 K) owing to its severe lattice distortion arose by entropy enhancement. As a result, the figure of merit reaches as high as 1.08 at 773 K for Cu ₃InSnSe ₅. Furthermore, electronic band engineering is adopted to enhance the carrier concentration and m* of Cu ₃InSnSe ₅ via the substitution of In for Sn, resulting in ∼28% enhancement in power factor, ∼21% increment in ZT (1.31 at 773 K), and ∼10% enhancement in average ZT (∼ 0.67 at 473 – 773 K) for Cu ₃In _1.01Sn _0.99Se ₅ compared with Cu ₃InSnSe ₅ itself. Our work shows Cu ₃InSnSe ₅ should be a promising candidate for thermoelectric power generation at medium temperature.