They are extremely thin, glow in brilliant colors and can even be printed on flexible films - electroluminescent QD LED displays. What makes them so special are the inks they are printed with: innovative quantum materials (quantum dots, QD) make it possible for each pixel of a display to emit light of a defined color when a current is applied. The new electroluminescent QD-LED displays promise to be energy-saving, efficient and cost-effective. Above all, the elimination of backlighting makes the electroluminescent QD-LED displays very thin.

As part of the EU project Hi-Accuracy, scientists at the Fraunhofer IAP are working with eleven partners to develop materials and methods for the production of high-resolution and flexible displays. Novel inks based on quantum materials and printing processes for electroluminescent QD-LED displays are being developed to make them even more powerful and efficient than before. The goal: a display resolution of more than 300 ppi. To achieve this, the electrohydrodynamic jetting process (EHDJET) will be optimized in the future, a method with which the QD LED inks can be printed with an accuracy of four micrometers.

Fast troubleshooting during the printing process

Quality control also plays an important role in the printing process. Is the layer morphologically flawless? Are there irregularities in the layer thickness? What is the chemical composition? In future, manufacturers who use other coating processes such as atomic layer deposition (ALD), roll-to-roll coating in a vacuum or sintering processes in addition to printing processes should be able to answer these questions during the coating process or immediately afterwards.

As part of the EU project NanoQI, the Fraunhofer IAP research team, together with nine partners from industry and science, is developing a very fast and highly sensitive inline measurement technique to detect the quality of thin films. The information from three characterization methods is combined for this purpose: X-ray diffraction (XRD), X-ray reflectometry (XRR) and hyperspectral imaging (HSI).

Hyperspectral imaging is being further developed at the Fraunhofer IAP. This uses a hyperspectral camera that records the entire light spectrum from 400 nm to 960 nm during measurement. The team compares the recorded data with X-ray measurements and thus draws conclusions about various quality characteristics of the coatings. This enables the HSI to be calibrated so that X-ray measurements can be dispensed with completely in future and only HSI technology can be used. It offers a major advantage for industrial customers as it can be easily integrated into existing production facilities and does not require any radiation protection measures.