Ag-added Ge<inf>2</inf>Sb<inf>2</inf>Te<inf>5</inf> thin films were prepared by a pulsed-DC co-magnetron sputtering process using Ge<inf>2</inf>Sb<inf>2</inf>Te<inf>5</inf> and Ag targets. The effect of variation in Ag content through variable power on Ag target was studied on the microstructural and thermoelectric properties of as-deposited and fast annealed thin films at 400 °C in a vacuum. It is found that Ag addition induces enhancement in conductivity. When the power on Ag target is exceeded to a critical power, Ag<inf>8</inf>GeTe<inf>6</inf> phase formation occurs mixed with Ge<inf>2</inf>Sb<inf>2</inf>Te<inf>5</inf> cubic structure which limits the thermoelectric performance. Best conditions provide the films having a lowest electrical resistivity as 0.98 × 10<sup>−4</sup> Ω cm and the maximum power factor as 5.83 × 10<sup>−3</sup> W m<sup>−1</sup> K<sup>−2</sup>.
