Studies On Preparation And Properties Of Organic Thin-film Transistors Based On Inkjet Printing Small Molecule

Organic thin-film transistors has been of great attention in recent years. With the development of research, organic thin-film transistors performance is getting nearer to traditional inorganic thin-film transistors and extend application areas to flexible and folding electronics. Inkjet printing technology for organic thin-film transistors has been widely studied because of the merits of relatively low-cost and direct patterning capability compared with various solution-based fabrication processes.The research direction of this thesis is TIPS-pentacene based organic thin-film transistors. And we studied the optimizing process conditions, semiconductor nucleation behaviors, inkjet printing stability and a series of microscopic dynamics behaviors of TIPS-pentacene during inkjet printing process. The main contents include:(1) Inkjet printing of TIPS-pentacene was performed on UV-ozone, FDTS+UVozone, PVP and PETS modified substrates to research influential factor of size and reason of coffee-ring profile of single-drop film. The dispersion component of surface energy determined the diameter of single-drop film, and reducing polar component of substrate was an effective way to eliminate the coffee-ring effect. At last, we studied the optimum conditions on optimized surface (PVP) during inkjet printing, spacing setting and solvent selection. Current on/off ratio reached best value under proper spacing settings, and we selected tetralin as solvent because of its high boiling point and mild solubility.(2) We performed surface modification via UV-ozone, PVP, PETS, PTS to prepare surfaces with different surface polarity and morphology, then inkjet-printed TIPS-pentacene on the surface-treated substrates to fabricate bottom-contact organic thin-film transistors. We controlled semiconductor nucleation behaviors by adjusting the polarity of surface. On UV-ozone-treated and PVP-treated substrates, the high polarity of surface contributed to nucleation from the circumference. However, nucleation of TIPS-pentacene on surface with relatively low polarity would more likely to be occurred on interior liquid-solid interface, the grain boundary of the TIPS-pentacene was significantly reduced and the film coverage of TIPS-pentacene was markedly improved. In particular for PETS-treated surface, both subthreshold swing and threshold voltage of the OTFT were optimized because of the improvement of interface quality between TIPS-pentacene and the dielectric.(3) We analyzed the influenced factors of inkjet printing stability, and optimized the printing stability of tetralin by mixing another solvent in it based on the above factors. We described the relationship between jetting velocity and frequency to characterize inkjet printing stability and fabricated organic thin-film transistors by tetralin and mixed solvent separately. Experimental results showed mixing solvent was an effective way to improve printing stability and could also get relatively high device performance relative to single solvent to some extent.