Turning now to thin films, the record mobility measurement is more difficult to identify. Several papers report promising mobilities, even surpassing the 43.9 cm V -2 s -1 from Chen et al.: 35 cm 2 V -1 s -1 at 8.5×10 18 cm -3 via liquid iodisation of metallic Cu from Wang et al.; 35 cm 2 V -1 s -1 to 50 cm 2 V -1 s -1 at concentrations in the region of 1 × 10 18 cm -3 via iodisation of metallic Cu on crystalline Si substrates from Madkhali et al.; and 110 cm 2 V -1 s -1 at 1.1 × 10 18 cm -3 via MBE on crystalline Si from Ahn et al.. However, these measurements are from extremely thin films that have XRD peaks that can be attributed to the Cu and c-Si substrates, which themselves are extremely good charge carriers, making it difficult to decouple the transport properties of the substrate from those of the film. These results are therefore omitted from Figure . Storm et al. report consistently high thin film mobility via pulsed laser deposition (PLD, purple triangles in Figure ) over a wide range of carrier concentrations, which comprises the most reliable thin film data available in the literature. At the higher end of the carrier concentrations reported, films deposited from sputtering and liquid iodisation appear to approach the mobility limit arising from ionised impurity scattering, peaking around 10 cm 2 V -1 s -1 . Across the entire carrier concentration range, the experimental results fall within the IBTE+IMP limit (and critically fall outside the SERTA+IMP, i.e. AMSET, limit), justifying our approach.