Multifunctional Optical Outcouplers for Efficient and Stable White Organic Light-Emitting Diodes

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Lead Performer: Massachusetts Institute of Technology – Cambridge, MA
Partners: None
DOE Total Funding: $1,500,000
Project Term: April 1, 2020 – March 31, 2023
Funding Type: SSL R&D Funding Opportunity Announcement (FOA) (DE-FOA-0002090)

Project Objective

The principal challenge of this project is to fix the poor stability of phosphorescent blue OLEDs. To address this, the researchers demonstrate that a new type of optical outcoupling structure can control the lifetime of excitons within a given emissive material. The result paves the way to a new technology for OLEDs. The researchers term it “multifunctional” optical outcoupling, because they seek to extract light from OLEDs and also to engineer stability. The researchers will fabricate a novel plasmonic architecture that improves device stability by decreasing the excited-state lifetime of the emitters without drastically decreasing the light-extraction efficiency. Radiative excited states from phosphors will efficiently transfer energy to surface plasmon modes at a metal dielectric interface. To outcouple the light from the surface plasmon, the researchers will leverage a plasmonic phenomenon known as “extraordinary optical transmission,” wherein constructive interference between propagating surface plasmons dramatically reduces surface plasmon losses and enables transmission of light of up to 50% over ~150 nm bandwidth. The researchers will work with existing, state-of-the-art phosphorescent materials, improving their stability by a factor of 25 to L70=50,000 hours in a generic sky-blue OLED structure by reducing the exciton lifetime using a multifunctional optical outcoupler that extracts light from the device as well as engineering the stability. Stability is the key to employing higher-performance blue phosphorescent dyes and achieving IQE targets beyond the limiting performance of contemporary white OLED technologies.

Project Impact

Replacing fluorescence by phosphorescence in OLED-based solid-state lighting will surpass the U.S. Department of Energy’s efficiency target of 83% internal quantum efficiency (IQE) by 2022, simultaneously realizing the 2025 and 2035 efficiency targets in just three years. The ability of phosphorescent OLEDs to hit these efficiency targets is well-understood. The application of state-of-the-art phosphorescent materials will increase the quantum efficiency for blue emission, increasing the power efficiency of white OLEDs by 50%. The improvement in quantum efficiency alone will also achieve the 2035 target operating voltage of 2.7V at 10,000 lm/m2. The corresponding resulting energy savings are estimated to be 276 TBtu per annum, a substantial fraction of total energy consumption for lighting. The design is predicted to be cost-effective with a simple payback time of approximately three years.

Contacts

DOE Technology Manager: Brian Walker, brian.walker@ee.doe.gov   
Lead Performer: Marc Baldo, Massachusetts Institute of Technology