Promising thermoelectric performance in n-type AgBiSe2: effect of aliovalent anion doping

Abstract

Thermoelectric materials can convert untapped heat to electrical energy, and thus, it will have a significant role in future energy management. Recent industrial applications demand efficient thermoelectric materials which are made of non-toxic and inexpensive materials. Here, we report promising thermoelectric performance in halogen (Cl/Br/I) doped n-type bulk AgBiSe₂, which is a Pb-free material and consists of earth abundant elements. Aliovalent halide ion doping (2–4 mol%) in the Se²⁻ sublattice of AgBiSe₂ significantly increases the n-type carrier concentration in AgBiSe₂, thus improving the temperature dependent electronic transport properties. Temperature dependent cation order–disorder transition tailors the electronic transport properties in AgBiSe_1.98X_0.02 (X = Cl, Br and I) samples. Bond anharmonicity and disordered cation sublattice effectively scatter heat carrying phonon in the high temperature cubic phase of AgBiSe_1.98X_0.02 (X = Cl, Br and I), which limits the lattice thermal conductivity to a low value of ∼0.27 W m⁻¹ K⁻¹ at 810 K. The highest thermoelectric figure of merit, ZT, value of ∼0.9 at ∼810 K has been achieved for the AgBiSe_1.98Cl_0.02 sample, which is promising among the n-type metal selenide based thermoelectric materials.