Cu₃SbSe₄, a copper-based sulfide free of rare earth elements, has received extensive attention in thermoelectric materials. However, its low carrier concentration restricts its widespread application. In this study, a microwave-assisted solution synthesis method was used to produce samples of Cu₃SbSe₄, which enabled the formation of CuSe in situ and increased the yield. Through the use of first-principles calculations, structural analysis, and performance evaluation, it was found that CuSe can enhance the carrier concentration and that induced nano-defects have a positive effect on reducing the lattice thermal conductivity. Moreover, doping with Sn decreases the band gap of the system and moves the Fermi level into the valence band, increasing the carrier concentration to 1.15 × 10⁻²⁰ cm⁻³. Finally, the zT value of the Cu₃Sb_0.98Sn_0.02Se₄ sample was achieved at 1.05 at 623 K when the theoretical yield of a single synthesis was 10 mmol.

The previous works commonly adjust the carrier concentration through acceptor doping, but at the same time, the decrease of the Seebeck coefficient limits the further improvement of electrical properties in Cu₃SbSe₄-based materials. In this work, a microwave-assisted hydrothermal synthesis method was used to synthesize Cu₃SbSe₄/TiO₂ hollow microspheres. Part of TiO₂ participates in the reaction, replaces the Sb site of Cu₃SbSe₄ to form holes, and the rest is dispersed in the matrix in the form of the second phase. The first-principles calculations reveal that the doping of Ti significantly changes the band structure and phonon spectrum, thereby regulating carrier concentration while increasing phonon scattering. In addition, experimental results show that the energy filtering effect generated by the extra-mixed TiO₂ nano particles, which suppresses the decrease of Seebeck coefficient by acceptor doping. Consequently, the highest average power factor 897.5 μW m⁻¹ K⁻² and the zT peak value of 0.70 can be obtained in Cu₃SbSe₄/6%TiO₂ sample at 298–623 K. This work provides a new sight to improve the thermoelectric properties in Cu₃SbSe₄ through carrier concentration regulation and nano-phase composition.