Cu(In, Ga)Se2 (CIGS) films were deposited with intentionally incorporated Na2Se by a multi-step process onto SiO x /soda-lime glass substrates at elevated temperatures. The effects of sodium on film properties were investigated using X-ray diffraction, X-ray photoelectron spectroscopy and Hall effect measurements. By the addition of Na2Se, the hole concentration of the CIGS-based films (Ga/(In+Ga) ratio=0.37–0.39) increased dramatically to the 1016–1017 c m -3 range for a wide range of Cu/(In+Ga) ratios from 0.4 to 0.8. The increased hole concentration resulted in improved CIGS-based solar cells with efficiencies of 10–13.5% over an extremely wide Cu/(In+Ga) ratio range of 0.51–0.96. P-type Cu(In, Ga)3Se5 phase films with hole concentrations high enough to be used as absorber layers of photovoltaic devices were obtained for the first time by the Na control technique. The possibility of a new type of solar cell with a ZnO:Al/buffer/ p-Cu(In, Ga)3Se5 heterojunction structure is suggested.