In this paper, copper indium gallium diselenide (CIGS) thin films were deposited by a hydrazine-free solutions method. In the proposed method, acetylacetonate salts and Se powder were simply dissolved in triethylenetetramine under ambient conditions, respectively. These two solutions were mixed in a certain percentage to form the final CIGS precursor solution. CIGS films were obtained by a drop-coating method and subsequently annealed in nitrogen atmosphere. The facile formation of the precursor solution without the need to prefabricate nanoparticles enables a rapid and easy processing. The high stability of the solution in air further ensures the precursor preparation and the film deposition in ambient conditions without a glove box. The crystal structure, morphology, composition, electronic state, optical, and electrical qualities of CIGS films were characterized by XRD, SEM, EDS, XPS, UV–vis, and I–V. The easy preparation and low-cost nature of the proposed strategy make it quite attractive. The proposed synthesis strategy developed in this work may be used as a general process for low-cost deposition of CIGS film and may have bright application prospects in high-efficiency, yet low-cost, photovoltaic areas in the future.