Enhanced Light Outcoupling from OLEDs Fabricated on Novel Low-Cost Patterned Plastic Substrates of Varying Periodicity

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Lead Performer: Iowa State University – Ames, IA
Partners:

  • MicroContinuum – Cambridge, MA

DOE Total Funding: $1,428,992
Project Term: April 15, 2019 – April 14, 2021
Funding Type: SSL R&D Funding Opportunity Announcement (FOA) (DE-FOA-0001823)

Project Objective

This project will investigate fabrication methods of shallow corrugated plastic substrates for increased light extraction in OLEDs. The approach includes development of a buried metal mesh to improve conductivity into the OLED device. The fraction of the light generated in OLEDs that is emitted in the forward direction (i.e., the outcoupling factor ηout) is only ~17% to 20% in conventional bottom-emitting OLEDs. This is due to ~50% loss to internal waveguiding in the high refractive index [organics+indium tin oxide (ITO) transparent anode]/air interface plus excitation of surface plasmons at the flat metal cathode. Another ~30% of the light is waveguided through the substrate to its edges. While extracting the latter with a microlens array or a hemisphere is standard practice, recovering the internally waveguided light and mitigating plasmon loss inexpensively remain challenging. To broadly assess the best designs for enhanced light outcoupling, in addition to patterned OLEDs with different corrugation heights, devices, including multi-stack tandem OLEDs, will be fabricated also on substrates semi-flattened by ITO. To minimize trial and error, substrate and OLED designs will be guided by simulations, which will predict the optimal single- and multi-period structures and the maximal achievable ηout.

Project Impact

The project’s overall goal is to achieve ηout = 70% in white OLEDs using innovative corrugated light-extraction substrates fabricated in a simple, scalable, and low-cost method that is fully transferrable to roll-to-roll production. The corrugation results in light scattering and diffraction that minimize internal waveguiding by reducing total internal reflection at the [organics+ITO]/air interface and plasmon loss at the cathode.

Contacts

DOE Technology Manager: Brian Walker, brian.walker@ee.doe.gov
Lead Performer: Ruth Shinar, Iowa State University