Synergistic effect of In doping on electrical and thermal properties of Cu₂SnSe₃ thermoelectric system

Cu₂SnSe₃ has been considered as a potential thermoelectric material owing to its tunable transport properties and its phonon-glass-electron-crystal (PGEC) characteristics. Here, p-type pure and In-doped Cu₂SnSe₃ samples are synthesized by the solid-state sintering technique. Cubic structure with F4 ¯ 3 m space group is maintained for all the samples, and a linear increase in lattice parameter with increasing In concentration has been observed. The nature of electrical resistivity changes from semiconducting to metallic behavior for samples with x > 0.10. The decrease in both electrical resistivity and Seebeck coefficient with an increase in x is attributed to the increased hole concentration. Such a scenario is confirmed from the room-temperature Hall effect measurements. Indium doping also reduces the thermal conductivity of the Cu₂SnSe₃ system as a result of increased phonon scattering due to the mass fluctuation. Concurrently, enhancement of thermoelectric power factor (PF) and figure of merit (ZT) is achieved with In doping at Sn site of Cu₂SnSe₃. The maximum ZT of 0.04 has been exhibited by the sample with x = 0.25 at 400 K, which is six times higher than that of the undoped Cu₂SnSe₃.