OLEDs on planarized light outcoupling-enhancing structures in plastic

Journal Article · Wed Oct 12 00:00:00 EDT 2022 · Organic Electronics

DOI:https://doi.org/10.1016/j.orgel.2022.106648· OSTI ID:2418047

Dykstra, Erik ^[1]; Fralaide, Michael ^[2]; Zhang, Yu ^[2]; Biswas, Rana ^[2]; Slafer, W. Dennis ^[3]; Shinar, Joseph ^[2]; Shinar, Ruth ^[2]

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1. Iowa State Univ., Ames, IA (United States); OSTI
2. Iowa State Univ., Ames, IA (United States)
3. MicroContinuum, Inc., Watertown, MA (United States)

Light extraction from OLEDs remains a challenge. While consumer demand for OLEDs in display technology continues to grow as prices decline, commercial use of OLEDs in solid state lighting (SSL) applications is lagging due to low light extraction, which results in low efficiency. Previous studies have been directed toward increasing the light extraction factor η_out, but cost effective approaches that will enable high throughput and potential upscaling, as well as elucidation of the extraction process, are still lagging. One promising approach is the use of buried light extraction enhancing patterns that are planarized with a high refractive index (RI) layer. When adding substrate mode extracting means, the highest external quantum efficiencies (EQEs) were achieved using a complex approach of planarized vacuum nano holes. Here we present η_out-enhancing planarized extraction structures (PES) in plastic. While plastic substrates currently present long-term stability issues and other drawbacks, as we show, they provide a tool for simple, inexpensive, and rapid generation of various enhancing structures that importantly can be transferred to the preferred rigid and flexible glass substrates. Moreover, plastic substrates are attractive for biomedical applications. The successful structures we present are easily scalable periodic corrugations, e.g., with pitch a ~ 4.25 µm and pitch/depth ratio a/h ~2.4 planarized by a layer of RI ~1.9, resulting in maximal EQEs exceeding 60% for a green OLED and 48.5% for a white OLED. Comparable increased EQEs were achieved for structures with a ~ 15 and 16 µm, and a/h ~ 2.1 and 4, respectively. Enhanced extraction was also observed with a very simply fabricated quasiperiodic nanohole array, and surprisingly, with a random shallow design. The latter is at variance with simulations based on diffraction only. Results are discussed in terms of a, h, and structural parameters together with scattering matrix simulations to assess the effect of various PES parameters and the nanoparticle-embedded planarizing layer on η_out. The experiments and simulations indicate contributions of diffraction, reflection, and scattering to EQE enhancement.

• Research Organization: Iowa State Univ., Ames, IA (United States); Univ. of California, Oakland, CA (United States)
• Sponsoring Organization: USDOE Office of Energy Efficiency and Renewable Energy (EERE); USDOE Office of Science (SC)
• Grant/Contract Number: AC02-05CH11231; EE0008724
• OSTI ID: 2418047
• Alternate ID(s): OSTI ID: 1894738
• Journal Information: Organic Electronics, Journal Name: Organic Electronics Journal Issue: C Vol. 111; ISSN 1566-1199
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
Materials Science
OLED light extraction
Physics
planarized extracting patterns
plastic substrates
scattering matrix simulations