Influence of the Densification Process on the Thermoelectric Properties of p-Type SnSe Co-doped with Na and Cu as well as Na and Ag

SnSe has been at the forefront of thermoelectric material research ever since its single crystal was reported to exhibit record-breaking peak zT values in excess of 2 along two directions some 10 years ago. Recent reports indicated the importance of the processing parameters for its transport properties, notably including the purification methods to remove oxide impurities. Here, we investigated the different influences of different consolidation methods on the properties including the stability of SnSe using different p-type dopants, comparing hot pressing with spark plasma sintering. Ultimately, we were able to achieve very comparable results with hot pressing as with spark plasma sintering, which bodes well for the upscaling of the process in industrial settings. In fact, the highest zT value of 0.96 at 673 K was obtained for a hot-pressed sample codoped with Na and Ag. Notably, the Ag-containing samples exhibited higher zT values than those with Cu. However, since all samples began to exhibit cracks after the measurements and inconsistently changing thermoelectric properties, the stability of these materials needs to be improved before any potential usage in a thermoelectric device.