Copper ion diffusion by solid solution treatment advancing GeTe-based thermoelectrics

Coinage metals Cu and Ag are widely reckoned as effective dopants in thermoelectric materials due to their ability to optimise carrier concentration while preserving high carrier mobility, attributed to their inherent dynamic features. Traditionally, Cu/Ag ions are introduced through eutectic reactions, which inevitably result in interstitial doping. Here, we develop an innovative solid solution doping strategy that enables targeted doping, whereby Cu ions exclusively occupy host lattice sites rather than interstitial sites. By combining first-principles calculations with in-situ experiments, we demonstrate that this targeted doping approach relies on ion diffusion and induces lattice renormalisation, effectively reducing lattice defects and suppressing hole concentration. Consequently, the 1 at.% Cu doped Ge_0.85Sb_0.10Te sample exhibits an exceptional figure-of-merit of 2.3 at 775 K along with a desirable average value of 1.4 scoping 300 to 775 K. The power density of the corresponding single-leg thermoelectric module is 2.23 W·cm^-2 under a temperature difference of 475 K. This work not only explains the kinetics behind dynamic doping behaviours, but also provide an original method to achieve high-quality functional materials with less lattice defects and a high carrier mobility.