Figure shows the explicit scattering rates at energies at and just below the valence band maximum. This confirms that ionised impurity scattering is the predominant scattering mechanism in CaCuP at room temperature. Figure compares the scattering rates at 1 × 10 18 cm -3 and 1 × 10 20 cm -3 , where a clear switch in the dominant scattering mechanism can be seen -polar optical phonons dominate at lower hole concentrations, and the mobility has a much stronger temperature dependence. Also shown is the effect of decreasing the grain size to 20 nm, which increases the scattering rate from grain boundaries, lowering the total mobility and therefore conductivity, as observed in experiment. We also present directional mobility data in Figure . Predicted hole mobility is almost four times greater in the xy-direction (in plane) compared to the out of plane (z-direction) mobility. This is as expected, considering the layered structure of CaCuP and the high dispersion that is confined to only two directions in the band structure. This anisotropy may explain why the electrical properties of the films with greater c-axis texturing are superior, when measured in the plane of the substrate.