Encapsulating fabric-based OLEDs

November 29, 2016 // By Julien Happich
Researchers from the Advanced Display & Nano Convergence Lab at KAIST, Korea, have unveiled a new encapsulation method to design fabric-based OLEDs with performance levels comparable to that of glass-based devices, while benefiting from the flexibility and mechanical characteristics of the fabrics.

Publishing their results in Advanced Electronic Materials under the title "Reliable Actual Fabric-Based Organic Light-Emitting Diodes: Toward a Wearable Display", the researchers disclose a multi-step planarization and encapsulation method including both organic and inorganic multi-layered moisture barriers.

The researchers started with polyester-fibre-based woven fabric substrates, 100μm thick, which they planarized via a dual-step lamination process. To smooth out the rough fabric structure (the wefts and warps of the interwoven yarns), they used a 20 to 40μm thick PU film made of a low viscosity layer on the bottom side laying against the bare fabrics, and a higher viscosity film on the upper side to create a reliable flat surface onto which to deposit their OLED structure.

a) The fabric-based OLEDs with planarization layers and multilayer barrier films. b) SEM image and c) FIB-SEM image of the device's cross-section.

First, the researchers proceeded to lay a multilayer barrier film on top of the prepared fabric, consisting of aluminium oxide (Al2O3) deposited by atomic layer deposition (and poly(vinylalcohol) (PVA) used as further planarization layers, with respective thicknesses of 30 and 250 to 300nm. Inverted top-emitting OLEDs were then stacked by thermal evaporation. To further protect the OLED and prevent contamination during their fabrication, multilayer capping layers consisting of N,N′-Bis(naphtanlen-1-yl)-N,N′-bis(phenyl)-benzidine (NPB)/zinc sulfide (ZnS)/NPB/ZnS were inserted in the stack by in-situ thermal evaporation before the deposition of the first Al2O3 layer of the top multilayer barrier film.