One such material is copper iodide, CuI, first discovered in 1907 by the "father of transparent conductors" Karl Bädeker, and now enjoying somewhat of a renaissance. It crystallises in the cubic zincblende structure below 643 K (Figure ), possesses an optical band gap of around 3 eV, displays native p-type conductivity, and consistently shows one of the highest figures of merit, Φ, for any p-type transparent conductor (over 60 000 MΩ -1 for S-doped CuI). It has a disperse, isotropic valence band maximum (Figure ), with an average light hole parabolic effective mass of around 0.21𝑚 𝑒 , indicative of reasonably high hole mobility. The valence band maximum is formed by the interaction of Cu 3𝑑 𝑡 2 and I 5𝑝 orbitals, while the conduction band minimum is formed by the interaction of Cu 4𝑠 with I 5𝑠 orbitals, as shown schematically in the molecular orbital (MO) diagram in Figure . Cu and I atoms in blue and green, respectively. Cu have tetrahedral coordination, shown in grey. Crystal structure plotted using VESTA. X W K L U W L K U X 6 (b) Electronic band structure of CuI. Calculated using the PBE0 hybrid functional with the inclusion of spin-orbit coupling (SOC). Plotted using SUMO. (c) Schematic molecular orbital (MO) diagram of CuI. Upon the inclusion of SOC, further splitting occurs on the 𝑡 2 -5𝑝 MOs into light and heavy hole channels and a spin-orbit split-off band, as seen in (b). In addition to its rather attractive electronic structure, the simplicity of CuI is another strong factor in its revival in popularity. Good quality thin films can be deposited via relatively straightforward techniques such as vaporising iodine onto thin films of copper (à la Bädeker), solid-and solution-based iodisation reactions, and ink-jet printing, while more advanced techniques such as pulsed laser deposition (PLD), molecular beam epitaxy (MBE), and magnetron sputtering are beginning to gain traction. Stability of films in air and to thermal cycling can be improved by encapsulation with amorphous Al 2 O 3 , to prevent the oxidation of Cu(I) to Cu(II). Single crystal growth of CuI is reported more sporadically and over a much narrower range of charge carrier concentrations. In terms of devices and applications, CuI has been successfully used in thin film transistors (TFTs) with high operational stability and efficiency, while CuI nano-particle inks have contributed to improvements in high resolution X-ray imaging technology. Despite this fashionable return to the forefront of p-type TCM research, the charge transport behaviour of CuI is poorly understood. Experimental reports show no clear trend between hole mobility and carrier concentration, while little computational work has been undertaken on this subject. In this work, the intrinsic limits of CuI as a high-mobility transparent conductor are investigated from first-principles calculations and state-of-the-art charge carrier transport modelling. The intrinsic defect chemistry and the effects of chalcogen doping are examined to estimate the window of achievable charge carrier concentrations in CuI. The different contributions to the overall scattering rate are analysed using two separate approaches, where it is found that scattering from phonons and ionised impurities dominate at either end of the charge carrier concentration range, respectively.