In Figure we show the calculated band alignment of CaCuP, and compare this to other popular p-type transparent conductors (left). The calculations predict an electron affinity of 4.0 eV and ionisation potential of 5.2 eV for CaCuP. P-type semiconductors typically have high-lying valence band maxima and conduction band minima, allowing the facile formation of holes while limiting the formation of n-type defects. This is compared to typical ntype materials, which tend to have a much larger electron affinity which drives occupation of the conduction band by electrons. The ionisation potential of CaCuP is relatively low, indicating that hole formation is easily achievable -indeed, films of CaCuP dis-play hole (Hall) concentrations on the order of 1 × 10 20 cm -3 . In fact, the ionisation potential is lower than that of CuI, which suggests that an overall higher concentration of holes could be achieved with an optimised deposition process. Ideally, the ionisation potential of a p-type contact material should match the ionisation potential of the semiconductor where holes are to be injected or extracted. On the right hand side of Figure , we demonstrate that this is the case for CaCuP when compared against the experimentally determined ionisation potentials for two semiconductors of high technological interest (Si and methylammonium lead iodide, MAPI) and an emerging phosphide solar absorber (ZnSnP 2 ). This indicates that CaCuP could integrate well into various types of devices using these materials. In particular, CaCuP could be a convenient hole transport layer in phosphide-based device stacks.