In addition to good valence band dispersion, an optical band gap exceeding 3.1 eV is required for transparent conductors, corresponding to the wavelength of visible photons. Varley and coworkers also compared the trends in band gap across oxides, sulfides, nitrides and phosphides, finding that the median empirically corrected fundamental density functional theory (DFT) band gap of the phosphides investigated was around 2 eV, roughly half that of the oxides. This presents a challenge for phosphides, and in general for non-oxide transparent conductors. However, achieving transparency in materials with a small fundamental band gap is possible. SnO is a bi-polar TCM with an indirect fundamental gap of 0.7 eV, but larger direct gap of 2.7 eV corresponding to the optical transitions, yielding semi-transparency in the visible region. Similarly, boron phosphide has an indirect gap of 1.8 eV but a much larger direct optical gap of 4.0 eV. The strong overlap of B 2p and P 3p orbitals at the valence band maximum (VBM) yields a hole effective mass of around 0.3m e , 14 and predicted hole mobility is in excess of 900 cm V -1 s -1 . This exceptional mobility is attributed to the low effective mass and very weak scattering by polar phonons, due to the low ionicity of BP. This is another advantage of non-oxide materials in general for p-type transparent conducting applications -bonding tends to be more covalent, generally leading to a decreased contribution of polar optical phonon scattering to the total scattering process. There are conflicting reports on the optical transparency of BP, as it seems to strongly depend on synthesis conditions, crystallinity, and epitaxial relationships with the substrate. A current state-of-the-art p-type transparent conducting material (TCM) is copper iodide (CuI), with a figure of merit surpassing that of many oxide based p-type TCMs. CuI possesses a direct band gap of around 3.1 eV, and has a doubly degenerate VBM with average hole effective masses of 0.3m e and 2.1m e for light and heavy holes respectively, indicating relatively good band dispersion. The copper vacancy is predicted to be the main source of conductivity under I-rich growth conditions, where it is not charge compensated by native n-type defects. Room temperature reactive sputtering deposition followed by heating in an iodine atmosphere led to a conductivity of 280 S cm -1 while retaining up to 85% optical transmission. Thin films of CuI have been trialled successfully as thin film transistors, while single crystals of CuI have recently been grown for the first time, capable of acting as a hybrid blue LED. The facile deposition, wide direct band gap, self-doping mechanism (under I-rich conditions) and absence of secondary phases make CuI a very attractive p-type transparent conducting non-oxide.