Direct printing of organic light emitting diodes on textiles

It is an international cooperation: The Institute for Interfacial Process Engineering and Plasma Technology IGVP at the University of Stuttgart and the Institute for Materials Research in Diepenbeek, Belgium, are working together on direct printing of organic light emitting diodes (OLEDs) on textiles. Both teams are persuaded, that smart textiles with light emitting properties open a whole new world of innovative textile applications. Additionally to the use as protective or safety clothing for road workers, police and fire departments, light-emitting textiles can also be used for indoor and outdoor design. Lighting wallpaper, tiles, textile banners or flags used for advertisement are among the wide variety of applications. Even healthcare products, such as light therapy are within reach.

OLED-Stapel aus ultradünnen Lagen / Quelle: Institute for Materials Research (IMO)

OLED-Stapel aus ultradünnen Lagen / Quelle: Institute for Materials Research (IMO)

To achieve light-emitting properties on textiles OLEDs are printed directly onto textiles. The OLEDs consist of four to six extremely thin layers ending up with a device stack of max. 0.5 micrometres and therefore maintain the flexibility and drapability of the textile substrate. Furthermore, they have a high brightness and a low power consumption. To protect these devices from the fast degradation resulting from contact with oxygen or water vapour, an encapsulation layer is applied on top.

As the roughness of most textile substrates is in the micrometres range, and the thickness of the encapsulation layers and the different layers in the OLED stack are in the nanometres rage, the surface properties of different smoothing layers, i.e. polyurethane PU or acrylate, is examined first.

In the next step, smoothing layers will be applied with the help of plasma techniques and their transparency, chemical composition and barrier properties regarding oxygen and water vapour will be measured. On top of this layer, the OLED stack will be fixed by using spin coating and evaporation techniques, and their resolving light output and luminous efficacy will be analysed. To finalize the complete stack, a last encapsulation is applied and the final properties of the device are defined and compared with reference devices on PET foil and glass substrates. Parameters are for example brightness, power consumption and efficiency.

Summary and conclusion of the German-Belgian joint research: Efficient OLEDs can be printed directly onto textile carriers. They offer a variety of different uses and applications.

Read more about “Smart textiles” in our Techtextil blog

Kirsten Rein

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