Thermoelectric materials can convert heat into electricity, not only to harvest electrical energy from waste heat such as in automotives, but also to enhance the output of solar-thermal-electric energy converters. The conversion efficiency of a material increases with increasing thermoelectric figure of merit. For large-scale applications, the conversion efficiency and thusly the figure of merit need to be enhanced for this technology to become economically viable.
Copper chalcogenides achieve in part even lower thermal conductivity - a desired characteristic of advanced thermoelectrics - via their deficiencies and Cu ion conductivity, which leads to a short mean free path of the phonons. Of course, long range ion conductivity needs to be prevented to avoid self-destruction of the device. Therefore, we added large cations like Ba<sup>2+</sup> into Cu chalcogenides to prohibit extended Cu ion movement, while retaining localized mobility and deficiencies to simultaneously create low thermal conductivity and long term stability.