Synergistic effects of water addition and step heating on the formation of solution-processed zinc tin oxide thin films: towards high-mobility polycrystalline transistors.

Thin-film transistors (TFTs) with high mobility and good uniformity are attractive for next-generation flat panel displays. In this work, solution-processed polycrystalline zinc tin oxide (ZTO) thin film with well-ordered microstructure is prepared, thanks to the synergistic effect of water addition and step heating. The step heating treatment other than direct annealing induces crystallization, while adequate water added to precursor solution further facilitates alloying and densification process. The optimal polycrystalline ZTO film is free of hierarchical sublayers, and featured with an increased amount of ternary phases, as well as a decreased fraction of oxygen vacancies and hydroxides. TFT devices based on such an active layer exhibit a remarkable field-effect mobility of 52.5 cm2 V-1 s-1, a current on/off ratio of 2 × 105, a threshold voltage of 2.32 V, and a subthreshold swing of 0.36 V dec-1. Our work offers a facile method towards high-performance solution-processed polycrystalline metal oxide TFTs.