Improving the applicability of organic light-emitting diodes through integrated nanostructures

The organic light-emitting diode (OLED) is a promising technology for a variety of applications, such as displays, large-area lighting, integrated sensing, smart packaging, and signage. OLEDs are thin-film devices comprising organic semiconductors, which allow for cost-efficient high-volume manufacturing using solution-based fabrications methods and therefore hold great potential towards disposable and recyclable electronic products. In this thesis, three different approaches to improve the applicability of OLEDs through integrated nanostructures are explored.

Nanostructuring the carrier substrate's outside surface provides a way to enhance light extraction as well as customize tactile and visual device perception. Here, a polymer coating containing tetrapodal zinc oxide nanoparticles and color pigments is investigated with respect to surface roughness characteristics and optical properties.

Electrical device properties can be altered by integrating nanostructures directly into the OLED semiconductor stack. In this work, periodic nanopatterning of a metal electrode is shown to improve charge injection into the organic semiconductor layer of a single-carrier device through local electric field enhancements. A current increase of up to 300 % is observed, exceeding the planar current injection limit and indicating a local transition to space charge limited operation.

Integration of a photonic crystal slab into the waveguide formed by the OLED can also lead to resonant light outcoupling. Here, a fabrication method is presented to create two-dimensional nanogratings with variable grating designs in the commonly used electrode material indium tin oxide. Furthermore, a novel device structure is investigated in which a fluorescent nanopatterned waveguide is placed outside the OLED for directional light emission leading to sharp angle-dependent outcoupling peaks in the emission spectra.


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