Facile one-pot synthesis of polytypic (wurtzite–chalcopyrite) CuGaS₂

Abstract: In this investigation, monodisperse CuGaS₂ nanoparticles intended for use as visible-light-absorbing materials were synthesized using a facile one-step heating method that involved dissolving the precursors copper chloride, gallium acetylacetonate, and thiourea in a solvent consisting of either oleylamine alone or a combination of oleylamine, oleic acid, and 1-octadecene. The shapes of the resulting nanoparticles were either elongated, polygonal, or a mixture of both, depending on whether the crystal structure of the nanoparticles was predominantly wurtzite, predominantly chalcopyrite, or a more balanced mixture of both wurtzite and chalcopyrite (i.e., the nanoparticles were polytypic: both wurtzite and chalcopyrite phases were present). The crystal structure of the synthesized nanoparticles was found to be influenced by the temperature and the solvent applied during synthesis. X-ray diffraction data for the nanoparticles indicated that applying a temperature of 270 °C or using oleylamine, oleic acid solvent, and 1-octadecene during synthesis tended to yield a chalcopyrite phase, whereas applying a somewhat lower temperature (210 °C) or using oleylamine alone during synthesis tended to result in a wurtzite phase. The chemical states of the compounds obtained at different temperatures and using various solvents, as well as their crystal structures, morphologies, and optical properties were characterized via X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy, ultraviolet–visible spectroscopy, and photoluminescence. Graphical abstract: Optical absorbance spectrum (red line) and photoluminescence spectrum (black line) of a CuGaS₂ solid solution, and applications of this material in optoelectronics (photos below the spectra)[Figure not available: see fulltext.]