Analysis and optimization of light outcoupling in OLEDs with external hierarchical textures

• Autores: Kovacic, Milan; Samigullina, Dinara; Bouchard, Felix; Krc, Janez; Lipovšek, Benjamin; Soldera, Marcos Maximiliano; Lasagni, Andres Fabian; Reineke, Sebastian; Topic, Marko
• Año de publicación: 2021
• Idioma: inglés
• Tipo de recurso: artículo
• Materia: OLED; outcoupling; laser processing; hot embossing
• Institución: Consejo Nacional de Investigaciones Científicas y Técnicas

Hierarchical textures (combining 2D periodic large and small micro textures) as an external outcoupling solution for OLEDs have been researched, both experimentally and by optical simulations. For the case of a red bottom emitting OLED, different hierarchical textures were fabricated using laser-based methods and a replication step and applied to the OLED substrate, resulting in an increased light outcoupling. Laboratory-size OLED devices with applied textured foils show a smaller increase in efficiency compared to the final large area devices. The results show that the full exploitation of textured foils in laboratory-size samples is mainly limited by the lateral size of the thin film stack area and by limited light collection area of the measuring equipment. Modeling and simulations are used to further evaluate the full prospective of hierarchical textures in large area OLED devices. Optimization of hierarchical textures is done by simultaneously changing the aspect ratios of the small and large textures and a potential of 57% improvement in EQE compared to devices without applied textures is predicted by simulations. Optimized hierarchical textures show similar outcoupling efficiencies compared to optimized single textures, while on the other hand hierarchical textures require less pronounced features, lower aspect ratios, compared to single textures to achieve the same efficiencies. Hierarchical textures also help in eliminating flat parts that limit outcoupling efficiency. Finally, the limiting factors that prevent higher outcoupling are addressed. We show that the dominant factor is non-ideal reflection from the organic thin film stack due to parasitic absorption. In addition, possible ways to further increase the outcoupling from a thick substrate are indicated.
Fil: Kovacic, Milan. University of Ljubljana; Eslovenia
Fil: Samigullina, Dinara. University of Ljubljana; Eslovenia
Fil: Bouchard, Felix. Technische Universität Dresden; Alemania
Fil: Krc, Janez. University of Ljubljana; Eslovenia
Fil: Lipovšek, Benjamin. Technische Universität Dresden; Alemania
Fil: Soldera, Marcos Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas. Universidad Nacional del Comahue. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas; Argentina
Fil: Lasagni, Andres Fabian. Technische Universität Dresden; Alemania
Fil: Reineke, Sebastian. University of Ljubljana; Eslovenia
Fil: Topic, Marko. University of Ljubljana; Eslovenia