New paper: Ultrastable glass emission layers make OLEDs more efficient and durable

Organic light-emitting diodes made from small molecular weight organic semiconductors are composed of multiple functional layers. These layers are in most cases amorphous assemblies of the molecular building blocks. In our joint paper with our collaborators of the Group of Nanomaterials and Microsystems (GNaM) at the Universitat Autònoma de Barcelona entitled ‘High-performance organic light-emitting diodes comprising ultrastable glass layers‘, we shed some light on the growth of these layers. The work is published in Science Advances. The molecules making up the amorphous layers do not necessarily fall into place perfectly so that over time (but these are very long times beyond the lifespan of an OLED) the molecules wiggle into a more compact assembly. This settling can be accelerated greatly if the molecules on the surface are given some extra energy to migrate. Providing excess thermal energy through an elevated substrate temperature, much more stable morphologies – called ultrastable glasses – are formed. The optimum condition for this growth is around 85% of the materials glass transition temperature. 

In our study we have tested this growth condition for four different phosphorescent emitters in one common device stack and found that both the external quantum efficiencies and device lifetimes significantly increased. The illustration below summarizes our work graphically. 

The full citation is: J. Ràfols-Ribé, P.-A. Will, C. Hänisch, M. González-Silveira, S. Lenk, J. Rodríguez-Viejo, S. Reineke, High-performance organic light-emitting diodes comprising ultrastable glass layers. Sci. Adv. 4, eaar8332 (2018). DOI: 10.1126/sciadv.aar8332.

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International TADF Symposium in Frankfurt is upcoming

On Thursday, September 7, 2017, the International TADF Symposium (organized by cynora GmbH) will take place in Frankfurt. It will be a packed one-day event with a tight focus on OLEDs based on thermally activated delayed fluorescence (TADF). The event will bring together leading industry and academia to share new results and discuss upcoming developments. You can find all the details about speakers and program on the events webpage. It is definitely a very good opportunity to get in touch with the people working on this exciting material development.

New paper: Transparent and color-tunable organic light-emitting diodes with highly balanced emission to both sides

In this paper entitled ‘Transparent and color-tunable organic light-emitting diodes with highly balanced emission to both sides‘  we demonstrate transparent, two-color, stacked OLEDs that allow for balanced top- and bottom-emission. Making use of ultra thin, composite metal electrodes, this design avoids the use of ITO, such that this architecture can be transferred to flexible substrates. Careful optical design made it possible that the luminance of the device is virtually identical to both viewing directions, which is a great improvement over many earlier device layouts.