Inge Verboven

Printing Smart Designs of Light Emitting Devices with Maintained Textile Properties

To maintain typical textile properties, smart designs of light emitting devices are printed directly onto textile substrates. A first approach shows improved designs for alternating current powder electroluminescence (ACPEL) devices. A configuration with the following build-up, starting from the textile substrate, was applied using the screen printing technique: silver (10 µm)/barium titanate (10 µm)/zinc-oxide (10 µm) and poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate) (10 µm). Textile properties such as flexibility, drapability and air permeability are preserved by implementing a pixel-like design of the printed layers. Another route is the application of organic light emitting devices (OLEDs) fabricated out of following layers, also starting from the textile substrate: polyurethane or acrylate (10–20 µm) as smoothing layer/silver (200 nm)/poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate) (35 nm)/super yellow (80 nm)/calcium/aluminum (12/17 nm). Their very thin nm-range layer thickness, preserving the flexibility and drapability of the substrate, and their low working voltage, makes these devices the possible future in light-emitting wearables.

Steering the Properties of MoOx Hole Transporting Layers in OPVs and OLEDs: Interface Morphology vs. Electronic Structure

The identification, fine-tuning, and process optimization of appropriate hole transporting layers (HTLs) for organic solar cells is indispensable for the production of efficient and sustainable functional devices. In this study, the optimization of a solution-processed molybdenum oxide (MoOx) layer fabricated from a combustion precursor is carried out via the introduction of zirconium and tin additives. The evaluation of the output characteristics of both organic photovoltaic (OPV) and organic light emitting diode (OLED) devices demonstrates the beneficial influence upon the addition of the Zr and Sn ions compared to the generic MoOx precursor. A dopant effect in which the heteroatoms and the molybdenum oxide form a chemical identity with fundamentally different structural properties could not be observed, as the additives do not affect the molybdenum oxide composition or electronic band structure. An improved surface roughness due to a reduced crystallinity was found to be a key parameter leading to the superior performance of the devices employing modified HTLs.

Optimizing the outcoupling efficiency and the radiation pattern of organic light emitting devices by inkjet printing lens arrays films

It is known that organic light emitting diodes (OLEDs) can reach an internal quantum efficiency close to 100 %1 . Outcoupling of the generated photons however is not that efficient resulting in an extraction efficiency of only around 20 %2 . This is mainly due to total internal reflection at the OLED-substrate and substrate-air interfaces. In recent literature1,3 , lenses are proven to be an adequate solution, but lens production techniques are complex, expensive and unsuitable for mass production. The aim of this research is therefore to investigate the development of a cost-effective lens array film by inkjet printing. These inkjet printed lenses are validated by pixelated OLEDs. Firstly, circular patterns of anisole are printed in a regular hexagon on PMMA-foil. Due to the coffee ring effect, reservoirs are formed in this foil which prevent the liquid lenses from merging. Afterwards these lenses, i.e. spherical droplets of NOA74, are deposited into these reservoirs and cured by ultraviolet light. Finally, the lenses are connected to printed pixelated OLEDs. The developed lens array film increases the OLED’s outcoupling efficiency by more than 20 % as is also expected from a theoretical study on these light extraction principles. The combination of the above-mentioned route for lens printing with the deposition of patterned OLED pixels, will not only improve the outcoupling to a large extend but will also help to develop OLEDs with a tailored emission pattern. A throughout understanding of the principles behind it will lead to optimized extraction efficiencies for large area printed OLED panels.

Direct Printing of Light-Emitting Devices on Textile Substrates

Smart textiles are a rapidly expanding field in the world of textiles, announcing a new and intriguing era. Different functionalities can be added to the textile to make the textile smart and intelligent. One of these functionalities is the addition of light-emitting layers or devices that can be incorporated into the textiles. These light-emitting textiles find a broad application in the field of interior and exterior design and wearable applications. Depending on the application, two light-emitting devices, the alternating current powder electroluminescent (ACPEL) device and the organic light emitting diode (OLED), both consisting out of a stack of thin layers, can be directly printed on top of the textile substrates. With its relatively high AC voltage of 50–200 V, the ACPEL device is more suited for interior and exterior applications while the OLED with a low DC voltage of 3–5 V is a perfect candidate for wearable applications. To maintain typical textile properties such as flexibility, breathability and drapability, different smart designs of the ACPEL devices are suggested, screen printed and analysed. More challenging is to apply the OLEDs on textile substrates. The very thin nanometre range layers make a planarizing layer to smoothen the textile surface indispensable. Different techniques such as spin coating, ultrasonic spray coating, inkjet printing and thermal evaporation are used to apply the complete OLED stack.