The combined mobility from IBTE and IMP acts as an upper limit to hole mobility in CuI, within which the presently available data from experiment falls. First, single crystal data is considered (orange stars in Figure ), which should represent the highest achievable experimental mobility and truest comparison to simulation, as only the intrinsic, material-dependent scattering processes should be present. It is well-known however that single crystal size, cleanliness and surface defects can all impact mobility measurements. Record single crystal mobility is reported by Chen et al., achieving a value of 43.9 cm 2 V -1 s -1 at a carrier concentration of 4.3 × 10 16 cm -3 in a sample of dimensions 15 × 10 × 1 mm. This is in the electron-phonon scattering limit, and suggests significant scope for improvement in mobility at low carrier concentrations. Other single crystals have been synthesised by Lvet al., obtaining a sample of similar size and carrier concentration but with a reduced mobility of 12.8 cm 2 V -1 s -1 , and Matsuzaki et al., achieving mobility up to 29 cm 2 V -1 s -1 at low concentrations (2.0 × 10 14 cm -3 ) and 19 cm 2 V -1 s -1 at carrier concentrations approaching the degenerate conductivity limit. By considering the POP scattering rate from AMSET as the dominant low concentration scattering mechanism, Chen's measurement exceeds the predicted mobility. It is reasonable to assume that this single crystal measurement is within the "low" carrier concentration regime, as a rough calculation of the Mott criterion using the parabolic (transport) band edge effective masses and the experimental dielectric constant indicates a carrier density of 8.5 × 10 17 cm -3 (1.65 × 10 18 cm -3 ). This failure of the SERTA to describe the low carrier density experimental data-points was the first indication that a more sophisticated treatment of the e-ph scattering would be required for CuI.