The impact of the deposition process of the emitting layer on the internal structure of organic light-emitting diodes

Organic light-emitting diodes (OLEDs) continue to attract research interest due to their increasing applications in display and lighting markets. A current field of development is the application of solution-based deposition techniques for the organic layers. However, in general, corresponding devices do not yet reach the performance of OLEDs with vapor deposited materials. In the present work, we have used a model system with a sulfur- containing host material in the emission layer that can either be deposited by thermal evaporation or spin coating. The structure of the corresponding devices was analyzed by a combination of transmission electron microscopy and spatially resolved energy-dispersive x-ray analysis. To investigate the devices' cross section, wedge shaped, electron transparent lamellas were prepared by focused ion beam milling. Significant differences of the spatial distribution of sulfur have been observed in the devices.