Mitigation of Power Factor Degradation in Bi2Te3 Thin Films

For thin-film thermoelectric modules with electrodes deposited on the sides of the thermoelectric material, the diffusion of atoms from the electrode affects the module's performance. Long-term aging is crucial when the module is for practical applications. In this study, Bi2Te3 thin films with a highly preferred orientation were fabricated by a co-sputtering deposition method. Cu was used as the electrode because of its high electrical conductivity; it migrates through the Bi2Te3 film via surface and grain boundary diffusion. The diffusing Cu segregates at grain boundaries and forms a Cu2-xTe intermetallic compound on the sample surface. Contact resistivity at the interface between the Cu electrode and Bi2Te3 thin films substantially increases with aging time. Long-term aging unavoidably degrades the power factor (PF) of the pristine Bi2Te3 since n-type Bi2Te3 converts into p-type by the formation of antisite defects. The study shows that the diffusing Cu from the electrodes of the Cu/Bi2Te3/Cu module significantly mitigates the degradation of the PF after long-term aging.