Inducing High Power Factor in Cu2GeSe3-Based Bulk Materials via (Bi, Zn)-Co-doping

In this work, carrier concentration optimization and effective mass increase of Cu2GeSe3, which were considered to be a synergetic effect of electrical transport properties, were achieved by the co-doping of Bi and Zn on the Cu site. This effect led to a higher Seebeck coefficient of ∼307.76 μV K–1 at 723 K for the Cu1.988Bi0.01Zn0.002GeSe3 sample. This effect also resulted in a higher power factor of ∼8.66 μW cm–1 K–2 at 723 K and an average power factor of ∼6.29 μW cm–1 K–2 at the temperature range of 303–723 K for the Cu1.988Bi0.01Zn0.002GeSe3 sample, which were ∼135 and ∼196% larger than those of pristine Cu2GeSe3, respectively, and are among the highest value of the Cu2GeSe3-based sample. Benefiting from simultaneous optimization of the power factor, the maximum ZT of ∼0.75 for the Cu1.988Bi0.01Zn0.002GeSe3 sample at 723 K was obtained, which is ∼288% higher than that of Cu2GeSe3.