Enhanced Stability and Thermoelectric Performance in Cu1.85Se-Based Compounds.

Liquid-like copper selenium compounds have attracted considerable interest in recent years for their excellent thermoelectric performance, abundant element reserves, and low toxicity. However, the related applications are still limited due to the phase transition and precipitation of Cu under an external field. Here, the cubic Cu1.85Se-based compounds with suppressed phase transition and improved critical voltage (Vc) are first studied. In particular, Li/Bi co-doping effectively optimizes hole concentration and the ZTs are substantially improved from 0.2 in Cu1.85Se to 0.7 in Li0.03Cu1.81Bi0.04Se at 760 K. Meanwhile, the latter shows an outstanding Vc above 0.22 V at 750 K, which is the highest value in Cu2-xSe thermoelectric compounds to date. Moreover, S is alloyed in Li0.03Cu1.81Bi0.04Se to greatly reduce the thermal conductivity and the ZT is further enhanced to 0.9 for Li0.03Cu1.81Bi0.04Se0.9S0.1 at 760 K. Our work sheds light on a new strategy to realize good stability and enhanced thermoelectric performance, which provides a new direction for further research.