Quaternary Cu 2 ZnSnSe 4 particles, useful for low cost solar cell synthesis, were successfully prepared using sonochemistry assisted solid state synthesis method. The pathways of the reactions during the synthesis as a function of the annealing temperature were studied by X-ray diffraction and energy dispersive X-ray spectroscopy (EDS) with the identification of the intermediate binary phases (Cu–Se, Zn–Se, Sn–Se), ternary phases (Cu–Sn–Se, Cu–Zn–Se) and the eventual formation of the quaternary phase Cu 2 ZnSnSe 4 . The obtained particles were characterized by X-ray diffraction (XRD). Only the quaternary particles were analyzed by Ultraviolet–visible (UV–Vis) optical absorption spectroscopy. The results showed that the annealing temperature of 450 °C is optimal for the formation of the pure quaternary phase. However, the temperature range within which pure Cu 2 ZnSnSe 4 could be obtained was very narrow and Cu 2 ZnSnSe 4 decomposes to various binary and ternary phases as the temperature is increased above the stability range. UV–Vis absorption spectroscopy illustrated that the particles had high absorption of visible light and had a direct band gap around 1.2 eV. These findings demonstrated a low-cost and environmentally friendly method to synthesize CZTSe particles.