Thermoelectric performance of multiphase GeSe‐CuSe composites prepared by hydrogen decrepitation method

Summary Recently, lead and tellurium‐free GeSe chalcogenide‐based thermoelectric materials have been considered as an alternative for PbTe and GeTe because of their nontoxic and attractive properties. However, the reports on thermoelectric properties of GeSe are very limited with low power factor values. Herein, we report the effect of Cu substitution on mixed phase formation and thermoelectric performance of Ge1−xCuxSe (0.0 ≤ x ≤ 0.4) samples. In the prepared samples, the multiphases of orthorhombic/Imm2 Cu2GeSe3, cubic/Fm3m Cu2Se, hexagonal/P63mc CuSe, hexagonal/P63/mmc Cu8GeSe6, and orthorhombic/Pnnm CuSe2 were observed, due to incorporation of Cu in GeSe as confirmed by X‐ray diffraction analysis. The electrical resistivity of the samples decreased with x values due to the formation of Cu‐rich phases. Moreover, the mobility of GeSe increased by one order through Cu substitution resulting from the percolation effect in the sample with multiphases. A high‐power factor of 720 μW/K2m was achieved at 500 K for the Ge0.6Cu0.4Se samples with thermal conductivity (κL) of 1.47 Wm−1κ−1 at the same temperature which resulted in a high figure of merit (ZT) ~ 0.26, due to Cu‐rich multiphases in the sample. ZT of GeSe is significantly enhanced by multiphase. Cu substitution changes the phases in the material and the Cu‐rich phases modulate the carrier concentration which results in high ZT.