Synthetic Strategies, Thermal Stability, and Optical Properties for Nanostructured Famatinite with Cu-Site Doping

A copper–antimony–sulfide phase known as famatinite (Cu3SbS4), with desirable properties for photovoltaic and thermoelectric applications, has been synthesized using a solution-phase technique that is energy-efficient and surfactant-free. The modified polyol process produced phase-pure nanoparticles (20–30 nm diameter) and allowed the facile incorporation of a range of Cu-site dopants (Fe, Ni, Zn, and Mn). Synthetic optimization identified the ideal reaction time and temperature to produce phase-pure famatinite and revealed covellite (CuS) as the primary growth intermediate. The effect of Cu-site dopants and nanostructuring on the thermal and optical properties was investigated. Thermogravimetric analysis and differential scanning calorimetry showed that doping the nanoparticles on the Cu-site improved thermal stability to be comparable with larger particles. Decomposition analysis by X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS) further demonstrated the stability of famatinite with Cu-site dopants and identified sulfur loss as a major factor in the phase transition of famatinite to tetrahedrite (Cu12Sb4S13) upon annealing. Optical characterization of famatinite revealed a direct ∼0.9 eV band gap regardless of dopant. Dispersibility of famatinite nanoparticles was tailored for different solvents by post-synthetic surface functionalization. The combination of thermal stability, favorable optical properties, and processability demonstrated herein affords famatinite materials with tunable properties for application in solar cells and thermoelectric devices.