Progress in Amorphous Transparent Conducting Oxide Thin Films

With the increasing wide application of organic or polymer substrates, amorphous transparent conducting oxides (a-TCOs) had been widely applied to thin-film transistors, polymer/organic solar cells, electrochromic devices, electromagnetic shielding and other areas due to the combined transparency and conductivity as well as stable properties, processing compatibilities with current technologies and free of post-annealing. A-TCOs films were not the amorphous counterpart of crystalline TCOs but prepared with special elements under certain conditions. After the brief introduction to the working principle of TCO, the even general amorphous transparent semiconducting oxide was addressed intensively. It was worth to note that compared with c-TCOs and classic silicon, the features of electronic structure of a-TCOs were the cations with special configuration (n-1)d10ns0. The stable amorphous structure and excellent properties can be conserved due to larger overlap integral between the adjacent atoms, high mobility and robustness. Particularly, the near range structure characterization such as the medium range order, band structure described by density of states and the metastability of amorphous structure and the related properties were introduced as well. Afterwards, the properties and features of N-type and P-type a-TCOs were exampled in details, especially the indium-based systems, such as excellent a-In-Zn-O films. Less example of P-type a-TCOs were shown as no general principle had been formed for that. Finally, many state-of-art applications including thin-film transistor are introduced. Based upon the current status and emerging trend, three potential research perspective directions of a-TCO have been delivered:(1) to further investigate non-indium based a-TCO; (2) to develop on the P-type TCO with novel principle and material systems; (3) to enable the alternative application that occupied by conventional silicon previously.