Inkjet-Printed Oxide Thin-Film Transistors Based on Nanopore-Free Aqueous-Processed Dielectric for Active-Matrix Quantum-Dot Light-Emitting Diode Displays

Inkjet-printed thin-film transistors (TFTs) for active-matrix light-emitting diode display are drawing much attention for the advantages of low material waste and simple fabrication processes without vacuum deposition and photolithography steps. Herein, for the first time, solution-processed quantum-dot light-emitting diode (QLED) array displays driven with the inkjet-printed oxide TFT backplane were realized and demonstrated using a general “solvent printing” method. To suppress nanopore formation in the thick oxide films, carbon-free aqueous inks were employed for gate dielectrics. No nanopore was found in the whole 120 nm-thick gate dielectrics. However, compared to the organic inks, the aqueous inks have very low viscosity, resulting in uncontrollable ink spreading especially in transline printing. The ink easily shrinks on the low-surface-energy area and spreads on the high-surface-energy area, leading to serious uniformity problems (the upper lines even break at the top of underlying lines). To solve the problem, a “solvent printing” method was employed to form coffee-line surface-energy patterns, which were uniform without shape distortion. The surface-energy patterns can restrain the ink spreading and tune the morphology of the printed films. As a result, multilayer TFT arrays with ideal shapes were achieved. The mobilities of the printed top-gate TFTs in the backplane array were 3.13 ± 0.87 cm2 V–1 s–1 for switching TFTs and 2.22 ± 0.38 cm2 V–1 s–1 for driving TFTs. Finally, an active-matrix red QLED character display based on the printed oxide TFT backplane and solution-processed QLEDs was demonstrated. The “solvent printing” method opens a general route for inkjet-printed multilayer electronic devices.