Inkjet Printing High-Resolution Patterning of Quantum Dot LEDs
ONE Lab: Giovanni Azzellino, Vladimir Bulović
Collaborators: Francesca S. Freyria, Igor Coropceanu, Moungi G. Bawendi
The high luminescence efficiency and uniquely size-tunable color of solution-processed semiconducting colloidal quantum dots (QDs) make them promising candidates as optically- and electrically-excited luminophores in energy-efficient, substrate-independent, high-color-quality solid-state lighting and thin-film display technologies. Recent advances in the design of electrically-driven QD-LEDs have pushed their external quantum efficiencies toward 20%, comparable to those of phosphorescent organic LEDs. However, the path of these devices to market is hampered by the difficulty of patterning the emissive quantum-dot layer. Existing prototypes are manufactured by spin-coating the colloidal QDs. Furthermore, the thermal budget of these materials remains low—heating them up decreases their photoluminescence efficiency.
Given all of these constraints, inkjet printing is a good candidate for making patterned QD-LEDs. This technology offers a new and unexplored technique for room-temperature, maskless patterning of quantum dot light-emitting devices.
In this project, we exploit droplet-on-demand inkjet technology to manufacture electroluminescent devices. We adopt both surface treatments and solvent engineering approaches to get rid of the “coffee-stain” effect and to deploy uniform and continuous spots of emissive quantum dots with a lateral resolution of ~10µm, using single-droplet print with a commercial inkjet printer. In addition, with the latest generation of hybrid QD-LED architectures, we show that both visible- and near-infrared-emitting QD-LEDs can be patterned with inkjet technology. We believe this work can open the door to high-resolution QD-LED displays.
Optical profilometry of an array of infrared core-shell PbS-CdS quantum dots inkjet-printed onto ZnO (scale bar is 50 μm)