White top-emitting organic light-emitting diodes with solution-processed nano-particle scattering layers
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A random scattering approach to enhance light extraction in white top-emitting organic light-emitting diodes (OLEDs) is reported. Through solution processing from fluorinated solvents, a nano-particlescattering layer (NPSL) can be deposited directly on top of small molecule OLEDs without affecting their electrical performance. The scattering length for light inside the NPSL is determined from transmission measurements and found to be in agreement with Mie scattering theory. Furthermore, the dependence of the light outcoupling enhancement on electron transport layer thickness is studied. Depending on the electron transport layer thickness, the NPSL enhances the external quantum efficiency of the investigated white OLEDs by between 1.5 and 2.3-fold. For a device structure that has been optimized prior to application of the NPSL, the maximum external quantum efficiency is improved from 4.7% to 7.4% (1.6-fold improvement). In addition, the scattering layer strongly reduces the undesired shift in emission color with viewing angle.
Schaefer , T , Schwab , T , Lenk , S & Gather , M C 2015 , ' White top-emitting organic light-emitting diodes with solution-processed nano-particle scattering layers ' Applied Physics Letters , vol 107 , 233301 . DOI: 10.1063/1.4937004
Applied Physics Letters
© 2015 AIP Publishing LLC. This work is made available online in accordance with the publisher’s policies. This is the final published version of the work, which was originally published at https://dx.doi.org/10.1063/1.4937004
The authors are grateful to Novaled GmbH (Dresden) for financial support and material supply. M. C. Gather acknowledges financial support from the Scottish Founding Council through SUPA.