Polycrystalline CuP 2+x films are semiconductors with native p-type conductivity. Their electrical properties are rather insensitive to elemental composition in the vicinity of the stoichiometric point, and only moderately affected by the annealing conditions. The thermal conductivity of a P-poor CuP 2 film is 1.1 W/Km at room temperature, confirming its potential applicability as a thermoelectric material. However, the hole conductivity of CuP 2 is too low to achieve a high power factor (and therefore a high zT value) without extrinsic doping. Furthermore, decomposition of CuP 2 into Cu 3 P and gaseous phosphorus at around 400 • C hinders high-temperature applications. Although stability issues are not mentioned in the CuP 2 single-crystal literature, our polycrystalline CuP 2+x films were only stable in ambient conditions for a few days. It is currently not clear if this issue is related to the porous morphology of our films, or if it is an intrinsic behavior of CuP 2 .