Combining Fluorescence and Phosphorescence to Achieve Very Long Lifetime and Efficient White OLEDs

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Lead Performer: University of Southern California – Los Angeles, CA
DOE Total Funding: $801,092
Project Term: October 1, 2017 – September 30, 2019
Funding Type: SSL R&D Funding Opportunity Announcement (FOA) (DE-FOA-0001613)

Project Objective

The use of solely phosphorescent emitters have led to high efficiencies for white OLEDs (WOLEDs). While this research has advanced the technology, it has fallen short of the DOE’s projected timeline for advances in WOLED performance. This project takes a different approach to achieving white electroluminescence, which involves the use of a combination of fluorescent and phosphorescent emitters. These hybrid fluorescent/phosphorescent WOLEDs will give markedly improved cell efficacy and lifetime. The project will use a combination of a blue fluorescent (fl) emitter and green/red phosphorescent (ph) emitters to cover the visible spectrum, resulting in a high efficiency (EQE > 25% and power efficiency > 100 lm/W), white emission with color rendering index > 90, and an L70 lifetime of > 50,000 hours. This will be accomplished through four basic project objectives, involving a range of materials and device development targets: developing novel fl dopant, ph dopant, host, and transport materials that lead to very high quantum (EQE > 25%) and power efficiencies (> 80 lm/W) in hybrid fl/ph WOLED structures and carrying out lifetime studies at each step of the development process, with an objective to meet the 2020 DOE target for lifetime, demonstrating L70 > 50,000 hours for a WOLED with a CRI > 90 at an initial brightness of 10,000 lm/m2

Project Impact

The research on hybrid fl/ph WOLED represents a true paradigm shift in WOLED development, utilizing both fl and ph emitters at the peak of their performance. This project will move the state of the art in WOLEDs close to DOE’s 2020 targets for WOLED lighting panels. The expected WOLED cell efficiency at project’s end is > 80 lm/W, CRI>90 and L70 of 50,000 hours at 10,000 lm/m2. The fl/ph WOLED eliminates many of the shortcomings of the all-phosphorescent device while providing an alternate route to high efficiency and long lived WOLEDs. This device employs a fl-emitting dopant to harness all electrically generated high-energy singlet excitons for blue emission, and ph dopants to harvest the remainder of lower-energy triplet excitons for green and red emission, maintaining the potential for unity internal quantum efficiency. This approach has the advantages of a stable white balance with current, a high efficiency at high brightness due to reduced geminate exciton recombination, and an enhanced lifetime due to the combined use of a stable fluorescent blue and long-lived phosphorescent green and red dopants in a single emissive region.

Contacts

DOE Technology Manager: James Brodrick, James.Brodrick@ee.doe.gov
Lead Performer: Mark Thompson, University of Southern California

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