Overlapping Nanostacks Enable Direct Printing of Freeform Organic LEDs

The process enables precise control of layer thickness through parameter tuning as confirmed by vertical scanning interferometry (VSI), yielding smooth and ho- mogeneous layers with surface roughness values down to 2.78 nm and tunable thicknesses between 19 nm and 45 nm.

A three-layer OLED stack (total thickness ≈ 90 nm) was printed and structurally characterized using focused ion beam scanning electron mi- croscopy (FIB-SEM) and time-of-flight secondary ion mass spectrometry (ToF-SIMS), revealing distinct, well-defined layer bound- aries. First functional tests demonstrated electroluminescence at 580 nm with an operational lifetime of at least 20 min. Despite the lack of encapsulation, the OLEDs remained stable under ambient conditions with a shelf life of up to 9 days.