Cu(In,Ga)Se-2 (CIGS) nanoparticles as a precursor material of a thin absorber layer for the CIGS based solar cells were synthesized by the relatively simple colloidal process. CIGS nanoparticles of 15-80 nm in diameter were obtained by reacting a mixture of Cul, InI3 and GaI3 in pyridine with Na2Se in methanol at 0 degrees C in nitrogen atmosphere with mechanical stirring. As the reaction time increased from 0 to 1 min. the size of nanoparticle decreased, showing a minimum at 1 min. (about 15 nm in diameter with very small size distribution). Further increase in the reaction time resulted in an increase in the nanoparticle size. The change in the size of CIGS nanoparticles with the reaction time was analyzed in terms of the effects of mechanical stirring on the concentration distribution of solute, i.e., CIGS nuclei, in the colloidal solution, and hence on the nucleation and the subsequent growth processes of the CIGS nanoparticles. (c) 2006 Elsevier B.V. All rights reserved.