The quality of CuGaTe2 (CGT) thin films elaborated by close spaced vapor transport technique has been studied as a function of the source temperature (TS), iodine pressure (PI2) and the amount (XCu) of pure copper added to the stoichiometric starting material. A thermodynamic model was developed for the Cu–Ga–Te–I system to describe the CGT deposition. The model predicts the solid phase composition with possible impurities for the operating conditions previously mentioned. The conditions of stoichiometric and near-stoichiometric deposition were determined. The value of TS must range from 450 to 550°C for PI2 varying between 0.2 and 7kPa. Adding an amount up to 10% of pure copper to the starting material improves the quality of the deposit layers and lowers the operating interval temperature to 325–550°C. These optimal conditions were tested experimentally at 480°C and 500°C. The X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy have proved that the addition of pure copper to the stoichiometric source material can be considered as a supplementary operating parameter to improve the quality of CGT thin films.