Stacked White OLED With Hybrid Emission Layers
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Solution Overview
Problem
Current white organic light-emitting diodes (WOLEDs) face challenges with low color rendering index and efficiency roll-off at high brightness, along with exciton pile-up leading to reduced power/light-output efficiency due to triplet-triplet annihilation.
Innovation Solution
A WOLED design incorporating a cathode and an anode with at least two hybrid red/green emitting layers, including a mixed red/green emitting sublayer and an adjacent green emitting sublayer, and a blue emitting layer with a gradient blue emitter concentration profile or manager dopant to enhance charge balance and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a conventional white OLED structure is used, then the device can emit white light, but the color rendering index is low and efficiency rolls off at high brightness
Solution Approach 1:
The emissive layer is divided into multiple distinct layers (blue emitting layer, green emitting layer, red emitting layer) instead of using a single white emitting layer. Each layer is optimized for its specific color emission, allowing independent control of charge injection and exciton management to maintain high efficiency at various brightness levels.
Solution Approach 2:
Each emitting layer is given specific local properties: the blue layer uses a gradient emitter concentration profile, the green layer uses specific host-guest combinations, and the red layer uses appropriate dopants. This localized optimization of material properties enables each layer to operate at peak efficiency independently, preventing overall efficiency roll-off.
2Illumination intensity
If a conventional white OLED structure is used, then the device can emit white light, but the color rendering index is low
Solution Approach 1:
The device separates the emission into distinct spectral components (blue, green, red) through multiple emitting layers, each optimized for its wavelength range. This segmentation enables superior color rendering by providing pure, saturated emissions across the visible spectrum while maintaining high power efficiency through targeted material selection in each layer.
Solution Approach 2:
The patent employs composite material systems in each emitting layer, combining specific host materials with guest emitters and dopants tailored to each color. These composite structures enable simultaneous optimization of color rendering properties and electroluminescence efficiency for each spectral region.
3Productivity
If excitons are allowed to accumulate in the emissive layer, then more light can be emitted, but triplet-triplet annihilation increases and reduces power/light-output efficiency
Solution Approach 1:
By dividing the emissive structure into multiple layers, the patent distributes exciton generation and recombination events across different spatial zones. This prevents exciton pile-up in a single layer, reducing triplet-triplet annihilation while maintaining high overall light output through cumulative emission from all layers.
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 design achieves improved color stability and light efficiency with a higher color rendering index and extended device lifetime by balancing charge injection and reducing triplet-triplet annihilation.
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
An organic light emitting device (OLED) is provided that includes a cathode and an anode; a blue emitting layer; and at least two hybrid red/green emitting layers. One of the at least two hybrid red/green emitting layers is a cathode side, red/green emitting layer that is disposed between the cathode and the blue emitting layer. The second of the at least two hybrid red/green emitting layers is an anode side, red/green emitting layer that is disposed between the blue emitting layer and the anode. The OLED emits white light.