Copper oxide quantum dot ink for inkjet-driven digitally controlled high mobility field effect transistors

Copper oxide (CuO) quantum dots (QDs) having a diameter of 5–8 nm were synthesized by a simple solution process. The as-synthesized QDs showed a highly crystalline monoclinic phase of CuO with a bandgap of ∼1.75 eV. The CuO QDs were further formulated as an ink for inkjet printing of CuO field effect transistors (FETs). The ink-jetting behavior of the as-formulated ink samples showed that the CuO concentration and digitally controlled number of over-prints are important factors for optimizing the uniformity and thickness of printed films with smooth edge definition. To examine the electrical properties, CuO FETs were fabricated based on inkjet-printed line and dot patterns. The inkjet-printed CuO FETs showed a p-type semiconducting nature with a high carrier mobility of 16.4 cm2 V−1 s−1 (line-pattern) and 16.6 cm2 V−1 s−1 (dot-pattern). Interestingly, when microwave-assisted annealing was applied the FET showed ∼2 times higher mobility (i.e., 28.7 for line-pattern and 31.2 cm2 V−1 s−1 for dot-pattern), which is the best among the p-type inorganic based FETs.