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

Kovačič, Milan (author), Samigullina, Dinara (author), Bouchard, Felix (author), Krč, Janez (author), Lipovšek, Benjamin (author), Soldera, Marcos (author), Lasagni, Andrés Fabián (author), Reineke, Sebastian (author), Topič, Marko (author)

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.

• Language: English
• Keywords: optoelectronics, OLED, performance
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FE - Faculty of Electrical Engineering
• Publication status: Published
• Publication version: Version of Record
• Year: 2021
• Number of pages: Str. 23701-23716
• Numbering: Vol. 29, no. 15, art. 428021
• PID: 20.500.12556/RUL-144743
• UDC: 621.383.51
• ISSN on article: 1094-4087
• DOI: 10.1364/OE.428021
• COBISS.SI-ID: 73817859

Copyright

"© 2021 Optical Society of America. Users may use, reuse, and build upon the article, or use the article for text or data mining, so long as such uses are for non-commercial purposes and appropriate attribution is maintained. All other rights are reserved." (Datum opombe: 10. 3. 2023)

• Publication date in RUL: 10.03.2023

Record is a part of a journal

• Title: Optics express
• Shortened title: Opt. express
• Publisher: Optica
• ISSN: 1094-4087
• COBISS.SI-ID: 8636438

Secondary language

• Language: Slovenian
• Keywords: optoelektronika, OLED, zmogljivost