Increased light outcoupling efficiency in dye-doped small molecule organic light-emitting diodes with horizontally oriented emitters

By J. Frischeisen, D. Yokoyama, Ayataka Endo, Chihaya Adachi, Wolfgang Brütting. 2011

215 citations recorded by the source corpus.

Abstract Small molecule organic light-emitting diodes (SM-OLEDs) are efficient large area light sources facing their market entry. However, a low light outcoupling efficiency of typically 20% still strongly limits device performance. Here, we highlight the potential of employing dye-doped emission layers with emitting molecules having horizontally oriented transition dipole moments. The effect of molecular orientation is explained by studying optical simulations that distinguish between horizontal and vertical dipole orientation. In addition, an experimental method that enables straightforward determination of dipole orientation in guest–host systems is presented and used for the analysis of two materials that are very similar except for their orientation. By measuring the external electroluminescence quantum efficiency of SM-OLEDs based on these materials, evidence is found that a mainly horizontal dipole orientation enhances light outcoupling by around 45%. Furthermore, the effect of orientation in SM-OLEDs offers many additional benefits concerning stack design and has fundamental implications for material choice.

Subfields: Electrical and Electronic Engineering, Polymers and Plastics

View Paper: https://www.semanticscholar.org/paper/c431088367a1bd2d8749611d9e24830943461f8c

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In Electrical and Electronic Engineering

1. S. Reineke
2. M. Gather
3. T. Schmidt
4. Wolfgang Brütting
5. J. Frischeisen
6. C. Mayr
7. B. Scholz

In Polymers and Plastics

1. M. Gather
2. S. Reineke

Citations in the corpus

• Device efficiency of organic light‐emitting diodes: Progress by improved light outcoupling (2013, methodology): “This effect has been known for many years in polymeric OLEDs [104], only very recently, however, we have been able to show that orientation effects also play a role in small molecule OLEDs fabricated by vacuum evaporation, where the fluorescent or phosphorescent dyes are embedded with only a few per”
• Recent advances in light outcoupling from white organic light-emitting diodes (2015, background): “45-fold efficiency increase.(78) While this first work was based on elongated fluorescent emitter molecules, it is less obvious that phosphorescent emitter complexes, which tend to have a more bulky molecular structure, can also show preferred molecular orientation.”