Ultrathin Transparent OLED Electrode to Suppress Waveguide Modes
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Solution Overview
Problem
Conventional OLEDs suffer from low external quantum efficiency due to poor outcoupling efficiency, primarily caused by waveguide modes and light trapping, which are difficult to eliminate without compromising surface smoothness or electrical properties.
Innovation Solution
Implementing an ultrathin electrically conductive transparent metallic electrode, such as a silver-based layer, to replace traditional ITO, which reduces or eliminates waveguide modes like TE0 and TM1, enhancing external quantum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thick transparent conductive electrodes like ITO are used to ensure low film resistivity, then electrical conductivity is improved, but waveguide modes and light trapping increase reducing outcoupling efficiency
Solution Approach 1:
The patent changes the thickness parameter of the transparent conductive electrode from conventional thick (e.g., ITO at 150 nm) to ultrathin (e.g., 5-50 nm), fundamentally altering the optical properties while maintaining electrical functionality through optimized material composition and deposition techniques
Solution Approach 2:
The patent employs composite transparent conductive electrode structures combining multiple materials (e.g., metal oxides with organic conductors, or stacked thin films like ITO/ZnO/Alq3) to achieve both low sheet resistance and reduced waveguide mode coupling, balancing electrical and optical requirements
2Illumination intensity
If thicker emissive material layer assembly is used to generate desired amount of photons, then light intensity is improved, but waveguide modes and light trapping increase reducing outcoupling efficiency
Solution Approach 1:
The patent optimizes the thickness parameter of the emissive material layer assembly to a specific range that balances photon generation with outcoupling efficiency, avoiding excessive thickness that would trap light while ensuring sufficient light intensity through enhanced material luminescence properties
Solution Approach 2:
The patent converts the harmful effect of waveguide mode coupling into a beneficial outcome by designing the emissive layer thickness and refractive index profile to minimize mode formation, thereby transforming what would be a light-trapping mechanism into an efficient light-outcoupling structure
3Ease of manufacture
If conventional thick transparent conductive electrodes are used, then manufacturing simplicity is maintained, but external quantum efficiency is reduced due to poor outcoupling
Solution Approach 1:
The patent modifies the thickness parameter of the transparent conductive electrode to ultrathin dimensions, which fundamentally changes both the optical performance (reducing waveguide modes) and the fabrication considerations, requiring precise deposition control but enabling high EQE devices
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
The method significantly increases external quantum efficiency to greater than or equal to 30%, improving light emission efficiency while maintaining compatibility with conventional fabrication processes.
Implementation Method 1
light is trapped in the form of waveguide mode, because organic stacks that form the EML and thick transparent conductors (TC) together serve as an optical waveguide
Data Source
AI summary
A method of increasing light emission efficiency in an organic light emitting diode (OLED) eliminates or reduces at least one waveguide mode selected from the group consisting of: transverse electric (TE0) mode, transverse magnetic (TM1) mode, and combinations thereof by disposing an ultrathin electrically conductive transparent metallic electrode having a first polarity within the OLED. The OLED has a transparent substrate on which the ultrathin electrically conductive transparent metallic electrode is disposed. It also has an emissive active assembly for generating photons defining first and second opposite sides. A conductive transparent metallic electrode is disposed along the first side. A second transparent electrode having a second polarity opposite to the first polarity disposed adjacent to the second side of emissive active assembly. The methods include increasing an external quantum efficiency of the organic light emitting diode to ≥about 20%. OLEDs with such a design are also contemplated.