OLED Emitter Energy Level Design for Exciplex Suppression
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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 and reduce device lifetime, especially when the exciplex is the lowest energy state.
Innovation Solution
Designing an OLED configuration where the emitter material is chosen such that exciplex formation between the host and emitter materials does not contribute to the emission spectrum, even when the exciplex is the lowest energy state, by satisfying specific energy level conditions and using a root mean squared (RMSD) function to quantify spectral differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the host and emitter materials are chosen to achieve narrow emission spectrum for saturated colors, then color saturation is improved, but exciplex formation occurs which contaminates the emission and reduces device lifetime
Solution Approach 1:
The patent applies parameter changes by carefully selecting and adjusting the energy level parameters (HOMO and LUMO levels) of the host and emitter materials. Specifically, the host material is designed with HOMO level between -5.0 to -6.0 eV and LUMO level between -2.0 to -3.0 eV, while the emitter material has HOMO level between -5.5 to -6.5 eV and LUMO level between -2.5 to -3.5 eV. These parameter adjustments ensure that the energy gap conditions prevent exciplex formation while maintaining narrow emission spectrum for saturated colors, thus resolving the contradiction between color saturation and device lifetime.
2Stability of the object's composition
If the host material is designed to stabilize the device, then device stability is improved, but exciplex formation can still occur and contaminate the emission spectrum
Solution Approach 1:
The patent converts the potentially harmful exciplex formation into a beneficial outcome by designing the energy level structure such that while exciplex states are formed, they lie above the emitter's S1 state energy level. This causes the exciplex states to decay radiatively through the emitter material rather than forming non-emissive traps. The host material's specific HOMO (-5.0 to -6.0 eV) and LUMO (-2.0 to -3.0 eV) levels are engineered to achieve this, transforming what would be a harmful contamination into a mechanism that maintains pure emitter-dominated emission while still providing device stability.
3Manufacturing precision
If the energy levels are adjusted to prevent exciplex contribution to emission, then emission purity is improved, but device complexity increases due to multiple material selection constraints
Solution Approach 1:
The patent applies segmentation by dividing the material selection process into distinct functional components with specific energy level ranges. The host material is segmented with HOMO level between -5.0 to -6.0 eV and LUMO level between -2.0 to -3.0 eV, while the emitter material is segmented with HOMO level between -5.5 to -6.5 eV and LUMO level between -2.5 to -3.5 eV. This segmentation creates clear, manageable selection criteria that simplify the otherwise complex material selection process, allowing systematic optimization of emission spectrum purity while controlling device complexity through structured parameter ranges.
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 approach allows for an OLED emission spectrum that is at least 95% similar to that of an OLED with an inert host, while suppressing exciplex contribution, leading to improved color saturation and device stability, particularly for blue phosphorescent emitters.
Implementation Method 1
The emitter material is a delayed fluorescent emitter
Implementation Method 2
The emitter and host materials in the organic emissive layer satisfy the following conditions: a≤ET−ΔE≤b; where ET is triplet energy T1 of the emitter material, which is the lowest T1 energy among all materials in the organic emissive layer; ΔE is the energy gap between the High HOMO energy and the Low LUMO energy
Data Source
AI summary
Disclosed is an OLED configuration that although comprises an exeiplex 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.