Cu₂SiSe₃ as a Self-Doped Thermoelectric

Thermoelectric materials can convert thermal energy into electrical energy, taking advantage of the waste heat generated during many industrial processes. Currently, some of the best performing materials are chalcogenides containing toxic elements such as PbSe and PbTe.^[1] Therefore, there is a need for research into new thermoelectric materials, which contain earth-abundant and non-toxic elements.<br/><br/>Kesterites, for example CuZnSnS (CZTS), have been shown to have lattice thermal conductivity lower than PbTe, and equivalent to PbSe, showing that a low lattice thermal conductivity can be achieved without the inclusion of heavy atoms by increasing the structural complexity of the material.^[2] However, generating sufficient charge carriers through doping is a challenge, due to the complex quaternary defect chemistry. Taking inspiration from the kesterites, we have computationally investigated the ternary Cu₂SiSe₃ as a potential thermoelectric, as it has been previously shown to be intrinsically p-type due to the high concentrations of copper vacancies.^[3] There is also a large dopability window to increase the concentration of charge carriers further.<br/><br/>In this work we use the AMSET^[4] code to calculate the electronic transport properties using the momentum relaxation time approximation and which when combined with lattice thermal conductivities calculated using Phono3py^[5], with force-constants fitted using the hiphive package^[6], enabling the calculation of the thermoelectric figure of merit, zT. A zT of 0.91 is predicted in a self-doped crystal at 800 K, increasing to &gt; 1.5 at higher carrier concentrations.<br/><br/><br/>[1] Xiang, H. et al., Adv. Sustain. Syst., 2022, 6, 2100457<br/>[2] Skelton, J. M. et al., A. APL Materials, 2015, 3, 041102<br/>[3] Nicolson, A. et al., J. Mater. Chem. A, 2023,11, 14833-14839<br/>[4] Ganose, A. M. et al., Nat. Commun., 2021, 12, 2222.<br/>[5] Togo A., Phys. Rev. B, 2015, 91, 094306.<br/>[6] Eriksson F., et al. Adv. Theory Simul. 2019, 2, 1800184