EU funded project Hi-Accuracy

From Hi-Response to Hi-Accuracy

The display industry dominates the global market for printed, flexible and organic electronics. Currently, the industry is looking for innovative ways to increase screen resolution and displayable color space in liquid processed displays. This requires the development of new printing methods and light-emitting material systems. 

In the predecessor project Hi-Response (GA No. 646296), the front plane of a single-color active-matrix (AM) OLED screen was printed using electrostatic jetting (ESJET). 

Hi-Accuracy aims to go several steps further. The research goal in the EU project is high-precision printing of conductive, semiconductive, resistive, dielectric and optical materials with a µm-scale accuracy for a range of organic and large area electronics (OLAE) applications. Specifically, a multicolor active-matrix quantum dot display (AM-QD-LED) will be fabricated, with both the front, and the complete backplane, fully liquid processed. To this end, eleven consortium members are contributing their expertise on five different printing technologies. The result will combine state-of-the-art materials and printing inks with scalable, cost-effective printing and coating processes. The advantages of printing processes are lower costs - through material savings and cheaper production equipment - and scalability.

Strength of the ALD barrier

Such high barriers can only be achieved with an alternating stacking arrangement of two different barrier materials (e.g. Al₂O₃ and TiO₂). The right materials (metal oxides), their layer thickness and the number of layers is crucial. The layers must be completely closed so that no point defects occur. We perform barrier tests using Ca mirrors.

BT.2020 color space of QDs

Synthesis of QDs in all three colors has already been achieved at Fraunhofer IAP. In the project, the challenge is to match the BT.2020 color space.

The  full width at half maximum should not exceed 35 nm. To achieve this, the multi-shell quantum dots must be manufactured with very precise size (the size determines the color) and very small size distribution (the size distribution determines the full width at half maximum). In addition, the shell must be electron-permeable so that the QDs themselves can illuminate. This makes the envelope fundamentally different from the very thick protective envelopes for QDs that are excited with light.

Fully printable EL-QD-LEDs

In close cooperation with the Humboldt University in Berlin, we are developing layer stacks for the EL-QD-LED devices. These must be fully printable. Moreover, since the ESJET pilot system has not yet been operated in a glovebox, processing must be able to take place in air.

ESJET printing of different materials

In the predecessor project Hi-Response, electrostatic jetting technology was used to print one material for all pixels. In the further development, three materials are printed specifically next to each other on the same component.

For the ESJET process, this means that we are improving the process in terms of reproducibility and target accuracy.

Another important aspect is the development of QD inks.