Modulating the Surface via Polymer Brush for High‐Performance Inkjet‐Printed Organic Thin‐Film Transistors

A strategy is reported to control the morphologies of inkjet-printed small organic molecule semiconductor by modifying printed surfaces with polymer brushes. Polystyrene (PS) brushes with different chain lengths from 1.66 to 7.35 nm are grafted onto a dielectric surface via surface-initiated atom transfer radical polymerization to form uniform, hydrophobic surfaces. Single droplets of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) are then inkjet-printed onto these PS brush-modified substrates. TIPS-pentacene crystals are obtained with different morphologies depending on the chain length of the PS brushes. Short PS chains behave like self-assembled monolayers on the dielectric surface such that small crystals are formed with random orientations. Longer PS chains become partially extended in the solvent altering ink spreading, contact-line pinning, solute migration, and ultimately crystallization. Large self-assembled crystals are generated with highly oriented structures. Organic thin film transistors are fabricated by printing single dots of TIPS-pentacene. The device based on PS brushes of 5.14 nm exhibits the optimal device performances with an average mobility of 0.35 ± 0.23 cm2 V−1 s−1. These results demonstrate that these polymer brushes provide a route toward further understanding inkjet-printing techniques for high-performance organic electronics.