In this paper, a new and simple method is described that does not use an autoclave to synthesize copper indium gallium diselenide (CuIn 0.5 Ga 0.5 Se 2 ) particles from the constituent elements. The process also does not require a post-synthesis selenization step. A solvo-thermal route is followed in which the constituent element powders are dissolved and made to react in a solvent such as ethylenediamine (ED), or triethylenetetramine (TETA). Crystal structure, morphology, composition, and particle size distribution of prepared particles were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), and dynamic light scattering (DLS), respectively. The band gap energies of the prepared particles were determined using an UV-VIS-NIR spectrophotometer. The results indicate that the solvent temperature and the synthesis time significantly affect the formation of single-phase CuIn 0.5 Ga 0.5 Se 2 and the crystallinity of the particles. Further, the measured band gap energy for the prepared particles is close to that of the bulk material. For example, the single-phase plate-like CuIn 0.5 Ga 0.5 Se 2 particles with an average particle size of 413.9 nm which can be successfully synthesized at a temperature of 250 Β°C in 15 h, have a band gap energy of 1.15 eV.