Towards Nanoscale OLED Pixels Based on Plasmonic Electrodes

Augmented Reality (AR) and Virtual Reality (VR) require miniaturized displays with ultrahigh pixel densities. When scaling down the pixel size towards the nanoscale, the 2D planar geometry of conventional organic light-emitting diodes (OLEDs) evolves into a significantly more complex 3D geometry governed by sharp nanoelectrode contours. These cause (i) spatially imbalanced charge carrier transport and recombination, resulting in a low quantum efficiency, and (ii) filament growth, leading to rapid device failure. Also, the power emitted by an OLED is unfavorably affected by miniaturization, whereby the emitted power quickly drops for subwavelength devices. Many studies in the past have tackled one or the other of these issues showing the strong interest in this topic. Yet, so far, a comprehensive solution of these problems is missing and thus, individually addressable nano-OLEDs have only been reported for laterally arranged pixels [1], which exhibit instable operation and are not relevant for technological applications. Here, we demonstrate an individually addressable vertically-stacked subwavelength OLED pixel based on a nanoscale electrode capable of supporting plasmonic modes [2]. We circumvent adverse nanoelectrode effects by selectively covering sharp electrode contours with an insulating layer, while utilizing a nano-aperture in flat areas of the electrode. We thereby ensure controlled charge carrier injection and recombination at the nanoscale and suppress filament growth. As a proof of principle, we first demonstrate stable and efficient hole injection from Au nanoelectrodes in hole-only devices with above 90 % pixel yield and longtime operation stability. As a result, we showcase the smallest ever individually addressable vertically-stacked OLED pixel (300 x 300 nm² footprint) with satisfactory quantum efficiency (1%) and long lifetime based on an emitting metallic nanoantenna electrode. This highlights the potential to further leverage plasmonic nanoantenna effects for enhancing the performance and functionality of nano-OLEDs, as well as in many other (opto-)electronic devices, such as photodetectors, photovoltaic cells or photodetectors.

[1] P. Grimm, S. Zeißner, M. Rödel, S. Wiegand, S. Hammer, M. Emmerling, E. Schatz, R. Kullock, J. Pflaum, B. Hecht, Nano Lett., 2022, 22, 3, 1032–1038, DOI: https://doi.org/10.1021/acs.nanolett.1c03994

[2] C. Zhang, B. Ewald, L. Siebigs, L. Steinbrecher, M. Rödel, M. Emmerling, J. Pflaum, B. Hecht, arXiv:2409.20080, 2024, DOI: https://doi.org/10.48550/arXiv.2409.20080