OLED Emitter Orientation for Higher Photon Outcoupling
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Solution Overview
Problem
Existing OLEDs suffer from significant photon loss due to surface plasmons and waveguide modes, resulting in inefficient outcoupling of emitted light.
Innovation Solution
Incorporation of heteroleptic compounds with a specific orientation, where the C2 symmetry axis of the compounds is perpendicular to the substrate, and homoleptic compounds with a C3 symmetry axis oriented perpendicularly, to control the direction of photon emission and enhance outcoupling efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional OLED structures are used, then device simplicity is maintained, but photon outcoupling efficiency is low due to surface plasmon and waveguide mode losses
Solution Approach 1:
The patent changes the molecular orientation parameter of the emissive compounds from random/isotropic to highly anisotropic with specific symmetry axes (C2 or C3) perpendicular to the substrate. This parameter change in molecular arrangement modifies the transition dipole moment orientation, directing photon emission preferentially perpendicular to the substrate surface, thereby reducing waveguide mode losses and improving outcoupling efficiency without adding external optical structures
Solution Approach 2:
The patent employs asymmetric molecular designs using heteroleptic compounds (with different ligands LA and LB) or specifically oriented homoleptic compounds with defined symmetry elements. The C2 or C3 symmetry axes are deliberately oriented perpendicular to the substrate, creating an asymmetric emission pattern that favors perpendicular photon propagation over parallel propagation, thus reducing losses to surface plasmons and waveguide modes
2Loss of energy
If external outcoupling structures like micro-lens arrays are added, then photon extraction is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The emissive compounds themselves serve the dual function of light emission and optical direction control. By incorporating compounds with specific molecular symmetries (C2 or C3 axes perpendicular to substrate) directly into the emissive layer, the system self-regulates photon emission direction without requiring external optical elements. This self-service approach eliminates the need for micro-lens arrays or other complex outcoupling structures, simplifying manufacturing while maintaining high extraction efficiency
3Loss of energy
If isotropic emitters are used, then manufacturing is simpler, but outcoupling efficiency is reduced due to random photon emission directions
Solution Approach 1:
The patent changes the molecular orientation parameter from isotropic (random) to highly anisotropic with defined symmetry axes. By selecting compounds with C2 or C3 symmetry and orienting these symmetry axes perpendicular to the substrate, the emission pattern changes from omnidirectional to preferentially perpendicular, improving outcoupling efficiency by reducing losses to surface plasmons and waveguide modes that dominate when emission is random
Solution Approach 2:
The patent applies local quality control by ensuring that the emissive compounds in the emissive layer have specific local molecular orientations with their C2 or C3 symmetry axes perpendicular to the substrate. This localized orientation control at the molecular level creates a macroscopic effect where photon emission is preferentially directed perpendicular to the device surface, improving outcoupling without requiring complex external structures
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 orientation significantly enhances the outcoupling efficiency of OLEDs, reducing the need for external structures like micro-lens arrays and enabling high external quantum efficiency.
Implementation Method 1
OLEDs make use of thin organic films that emit light when voltage is applied across the device
Implementation Method 2
One application for phosphorescent emissive molecules is a full color display
Data Source
AI summary
Organic light emitting devices incorporating a film of metal complex emitters that are oriented with their transition dipole moment vectors oriented parallel to the device substrate enhances the outcoupling and eliminate the need for micro-lens arrays, gratings, or other physical extraneous outcoupling methods.