Rising concerns over climate change and dwindling non-renewable resources have led to increased emphasis on developing technologies to improve energy sustainability and to meet growing energy demand. Since more than 60 % of the energy used worldwide is wasted as heat, thermoelectric generators (TEGs), which can extract electrical energy from a temperature gradient, are currently the subject of intensive research. TEGs are easily scalable to a range of sizes for applications including in the automotive, manufacturing and nuclear industries, and can thus potentially improve energy sustainability across a wide range of sectors. The performance of a thermoelectric material in a TEG is typically expressed by the dimensionless figure of merit 𝑍𝑇: