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Low-Temperature Solution-Processed Soluble Polyimide Gate Dielectrics: From Molecular-Level Design to Electrically Stable and Flexible Organic Transistors.

Aromatic soluble polyimides (PIs) have been widely used in organic field-effect transistors (OFETs) as gate dielectric layers due to their promising features such as outstanding chemical resistance, thermal stability, low-temperature processability and mechanical flexibility. However, the molecular structure of soluble PIs on the electrical characteristics of OFETs have not been fully understood yet. In this work, the material, dielectric and electrical properties are evaluated to systematically investigate the chemical structure effect of aromatic dianhydride and diamine monomers on the device performance. Four soluble PIs based on hexafluoroisopropylidenediphthalic anhydride (6FDA) and 5-(2,5-dioxytetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, in which monomeric precursors containing different backbones, side groups, and linkages, were employed to compare the chemical structure impact. The dielectric properties, which significantly affect to the charge transport and crystallinity of OSC thin films, clearly depended on the soluble PI types as well as surface energy and thermal stability. Furthermore, the electrical characteristic measurement and parameter extraction of OFETs based on TIPS-pentacene revealed that the 6FDA-based soluble PIs, which lead to high field-effect mobility, near-zero threshold electric-field, and outstanding electrical stability under bias stress, are the most promising gate dielectric candidates. Finally, low-temperature solution-processed OFETs are successfully integrated with ultrathin flexible substrates and they exhibit no significant electrical performance loss after mechanical flexibility tests. This work presents a step forward to the development of soluble PI gate dielectrics for flexible electronic devices with high device performance.