Charge transport in solution-processed zinc tin oxide thin film transistors

Zinc oxide-based transparent amorphous oxide semiconductors (TAOS) are strong contenders to replace amorphous and polycrystalline silicon for large area display backplanes due to their high electron mobility. To enable future roll-to-roll printed electronics, solution-processed fabrication methods are needed. Here, we use low-temperature measurements from 77 to 300 K to quantitatively compare charge transport mechanisms and band-tail density of states of solution-processed zinc tin oxide (ZTO) thin film transistors fabricated with different film composition and annealing temperature. The devices exhibit percolation conduction with Fermi level pinning at high charge carrier concentrations. The shape and energy levels of band-tail states can be engineered by process and stoichiometry. For optimal amorphous ZTO film with Zn:Sn ink ratio of 7:3 and annealing temperature of 480 °C, the band structure exhibits Arrhenius and percolation energy values of 7 and 3 meV, respectively, better than those measured by others for vacuum-processed TAOS films, showing the potential of solution processing.