OLED Host Materials Suppressing Exciplex Formation
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Solution Overview
Problem
Organic light emitting diodes (OLEDs) face challenges in achieving a narrow emission spectrum for saturated colors and stabilizing the device, as exciplex formation can contaminate the emission spectrum and reduce device lifetime, especially for blue micro-cavity applications.
Innovation Solution
The OLED configuration includes an organic emissive layer with a phosphorescent or delayed fluorescent emitter and a host material, where the emitter and host satisfy specific energy conditions to suppress exciplex formation, ensuring the emission spectrum is at least 95% like that of an OLED with an inert host, and an enhancement layer with plasmonic material for energy transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional host materials are used in OLEDs, then the device can be fabricated with standard materials, but exciplex formation contaminates the emission spectrum and reduces device lifetime
Solution Approach 1:
The patent applies parameter changes by carefully selecting host materials with specific energy level parameters (HOMO and LUMO energies) that satisfy the condition a≤ET−ΔE≤b. This parameter optimization prevents exciplex formation while maintaining device performance, thereby improving reliability without sacrificing ease of manufacture
Solution Approach 2:
The patent introduces an intermediary approach by using specifically designed host materials that act as mediators between the emitter and the electrical excitation. These host materials transfer energy to the emitter without forming exciplexes, thus eliminating the harmful interaction while maintaining the energy transfer function
2Measurement precision
If the emission spectrum is narrowed for saturated colors, then color efficiency is improved, but device stability is compromised due to exciplex contamination
Solution Approach 1:
The patent uses parameter changes by optimizing the energy level parameters of host materials to prevent exciplex formation. This allows achieving narrow emission spectra for saturated colors while maintaining device stability, as the host-emitter energy level matching prevents harmful exciplex states that would otherwise form and degrade the device
3Illumination intensity
If blue phosphorescent OLEDs are developed, then color saturation is improved, but exciplex formation increases and reduces device lifetime
Solution Approach 1:
The patent applies parameter changes by selecting host materials with specific HOMO and LUMO energy parameters that satisfy the inequality a≤ET−ΔE≤b for blue phosphorescent emitters. This parameter optimization prevents exciplex formation in blue OLEDs, enabling high color saturation while extending device lifetime by eliminating the degradation pathway through exciplex states
Solution Approach 2:
The patent effectively makes the exciplex state a 'short-living' harmful intermediate that is prevented from forming in the first place. By optimizing host material parameters, the design eliminates the formation of these transient exciplex states that would otherwise lead to device degradation, thereby protecting the long-term stability of blue phosphorescent OLEDs
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration achieves a stable OLED with a narrow emission spectrum, suppressing exciplex contribution and enhancing device stability, particularly beneficial for blue phosphorescent OLEDs by expanding the energy level range and reducing exciplex formation, leading to improved color efficiency and longer device lifetime.
Implementation Method 1
The enhancement layer comprises a plasmonic material exhibiting surface plasmon resonance that non-radiatively couples to the emitter material and transfers excited state energy from the emitter material to non-radiative mode of surface plasmon polariton
Implementation Method 2
The emitter is selected from the group consisting of a phosphorescent metal complex, and a delayed fluorescent emitter
Implementation Method 3
OLEDs make use of thin organic films that emit light when voltage is applied across the device
Data Source
AI summary
Disclosed is an OLED configuration that although comprises an exciplex that has an emission spectrum that is redder than the emission spectrum of the emitter, the emission from the exciplex is suppressed so that the overall OLED emission spectrum is still dominated by the emission of the emitter.