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Cu 2 Se is one kind of popular thermoelectric materials due to its performance of the phonon glass-electron crystal. However, the poor thermal stability limits its application. Regulating the distribution of the Cu+ by elemental dopant is a general method to solve the stability and to improve the thermoelectric performance. In this study, the Ag-doped β-Cu 2−x Se films were prepared by vacuum thermal evaporation method. The Cu+ distribution on the octahedral 32(f) sites in the Cu 2 Se crystal is tuned by the Ag content. It found that when the Ag content is 1.0%, the Cu+ and Ag+ contents in the 32(f) sites reach the maximum. In this case, the power factor of the film is 1750 μW·m−1·K−2 at 530 K. As the Ag content rises, the second phase of CuAgSe appears. This results in the decrease of the power factor. It shows that controlling the distribution of the Cu+ by the Ag dopant is conducive to improve the thermoelectric properties of the β-Cu 2−x Se films. • Occupancy increase of Cu+ and Ag+ in 32(f) sites decreases resistivity. • CuAgSe second phase increases carrier concentration and effective mass. • Power factor of Ag-1.0% film is maximum and 300% higher than that of Ag-0.0% film. [ABSTRACT FROM AUTHOR]