Inkjet Printing of an Electron Injection Layer: New Role of Cesium Carbonate Interlayer in Polymer OLEDs

Single-Step Inkjet-Printed Dielectric Template for Large Area Flexible Signage and Low-Information Displays

In recent years, the proliferation of smart gadgets has increased the demand for information displays; fortunately, organic light-emitting diodes (OLEDs) show great promise for use in display, lighting, and signage contexts. This research demonstrates inkjet printing of dielectric materials to provide maskless emission area patterning and electrical isolation for large-area OLEDs on flexible/rigid indium tin oxide (ITO)-coated substrates, avoiding the need for typical photolithography steps, including etching and lift-off processes. We have studied the impact of impinged droplets' velocity fluctuations, which are measured in relation to their interaction with the substrate, allowing for the determination of the drop diameter and shape. The inkjet parameters, such as pulse waveform, pulse voltage, and pulse width, are controlled to provide consistently repeatable ejection of dielectric ink droplets. The single-step patterning of complex designs with a minimum opening of 18 μm features is successfully printed with high fidelity. The effect of substrate temperature on the printed template/structure size and shape is explored. We have successfully demonstrated an ultralarge-area (120 × 120 mm2) OLED signage application on inkjet-printed dielectric template (IJPDt). Standard small-area OLEDs (4 × 4 mm2) achieved a maximum brightness of 24480 cd m-2 at 10 V and a maximum current efficiency of 17 cd A-1 with a low turn-on voltage of 2.7 V.

Three Destinies of Solution-Processable Polymer Light-Emitting Diodes under Long-Time Operation

The article describes three different ways of polymer light-emitting diode (PLED) degradation, caused by damage of the protective layer. The electroluminescence and charge-transport properties of a completely encapsulated diode, the diodes with a leaky protective layer and diodes without encapsulation were compared under long-time exploitation. The studied devices incorporated Super Yellow light-emitting poly-(1,4-phenylenevinylene) PPV copolymer as an electroluminescence component, and (poly-(3,4-ethylenedioxythiophene)–poly-(styrene sulfonate) (PEDOT:PSS) as a charge-transport layer between the indium tin oxide (ITO) anode and aluminum–calcium cathode. To analyze the PLED degradation mechanism regarding charge transport, impedance spectroscopy was used. The values of resistance and capacitance of the internal layers revealed an effect of applied voltage on charge carrier injection and recombination. The factors responsible for the device degradation were analyzed on a macromolecular level by comparing the plots of voltage dependence of resistance and capacitance at different operation times elapsed.