Slot die-coated blue SMOLED multilayers
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The key challenge in solution-processing efficient OLEDs is to realize the multilayer device architecture. We demonstrate that slot die coating is applicable to deposit small-molecule (SM) layers on top of each other without dissolving the underlying layer. A stack for a blue SMOLED is chosen comprising slot die-coated PEDOT:PSS, an SM emissive layer (EML) as well as an SM electron transport layer (ETL). The devices are fabricated in a sheet-to-sheet coating process with a slot die table coater under ambient conditions. While keeping the processing parameters constant for PEDOT:PSS and the EML, the composition of the ETL is varied. The choice of solvent for coating the ETL is crucial regarding wetting and dissolution of the underlying layer, solubility, surface roughness, and device efficiencies. Average roughness values down to 0.38 nm and peak to valley values around 10 nm were measured. Comparing device efficiencies of devices with and without ETL, an increase in efficiency with a factor up to 42 was achieved. In total, we show 135 blue SMOLEDs to demonstrate reproducibility.
KeywordsSlot die coating OLED SMOLED Multilayer Solution processed Organic electronics Drying Film morphology AFM
Electron transport layer
Hole blocking layer
Hole injection layer
Hole transport layer
The authors acknowledge financial support via the project Print OLED (Contract Number 13N10759) and POESIE (Contract Number 13N13692) of the Federal Ministry of Education and Research. We would like to thank all involved mechanics, assistants, and our students for contributing to this work as well as TSE Troller AG, Murgenthal, Switzerland, for technical support. The authors are also thankful for the support of the Light Technology Institute (LTI) of KIT as well as the Institute of Printing Science (IDD) of the Technical University of Darmstadt and InnovationLab GmbH, Heidelberg.
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