Famatinite Cu3SbS4 has attracted attention for its potential application in thermoelectric (TE) contexts. In this work, we report the impacts of co-substituting Ge and P for Sb on TE properties. Melting and heat treatment methods were adopted to synthesize samples of Cu3Sb1-x-yGexPyS4 (x ≤ 0.4, y ≤ 0.3). In this system, Ge functioned as an acceptor for doping a hole to the valence band, which led to enhancement of the TE power factor. Contrastingly, P barely altered the electronic structure. Furthermore, both Ge and P acted as point defects, which effectively decreased lattice thermal conductivity. The combined effects of the co-substitution gave rise to an enhanced dimensionless figure of merit, ZT, of 0.67 at 673 K.
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