OLED Multiple Emissive Layers Distribute Exciton Formation
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Solution Overview
Problem
Conventional organic light emitting devices (OLEDs) face inefficiencies due to exciton formation primarily at a single interface, leading to exciton annihilation and reduced internal quantum efficiency, especially in white OLEDs where excitons 'pile-up' at the emission layer, causing enhanced triplet-triplet annihilation and limited power efficiency.
Innovation Solution
The implementation of multiple emissive layers with different host and dopant materials, aligned energy levels, and specific layer configurations to create multiple exciton formation regions, allowing for expanded exciton generation and reduced annihilation, thereby enhancing internal quantum efficiency and power efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single emissive layer is used in OLED, then the device structure is simple, but exciton annihilation occurs at the emission layer interface leading to reduced internal quantum efficiency
Solution Approach 1:
The single emissive layer is divided into multiple separate emissive layers (first emissive layer, second emissive layer, third emissive layer), each with different host and dopant materials. This segmentation distributes exciton formation across multiple interfaces, preventing exciton pile-up and annihilation at a single interface, thereby improving internal quantum efficiency while maintaining reasonable device complexity
Solution Approach 2:
The patent transitions from a single-layer (one-dimensional) emissive structure to a multi-layer (three-dimensional stacked) emissive structure. By stacking multiple emissive layers with different energy levels, exciton formation is distributed across multiple spatial zones, reducing exciton density at any single interface and minimizing annihilation losses
2Reliability
If multiple emissive layers with different host and dopant materials are used, then internal quantum efficiency is enhanced by distributing exciton formation, but device complexity increases
Solution Approach 1:
Each emissive layer is designed with specific local properties: the first emissive layer has a first host material and first dopant with specific energy levels, the second emissive layer has a second host material and second dopant with different energy levels, and the third emissive layer has a third host material and third dopant. This local differentiation optimizes exciton formation at each interface while managing device complexity through systematic material selection
Solution Approach 2:
The patent employs composite material systems where each emissive layer combines specific host-guest material pairs with tailored energy levels. The first, second, and third emissive layers use different composite material combinations, creating a gradient structure that facilitates efficient exciton formation and energy transfer while maintaining manufacturability
3Loss of energy
If multiple emissive layers are implemented, then power efficiency is improved by reducing exciton annihilation, but manufacturing complexity increases
Solution Approach 1:
The emissive structure is segmented into multiple depositable layers, each potentially fabricated as a separate module. This segmentation allows for optimized deposition processes for each layer while maintaining overall power efficiency through the distributed exciton formation architecture
Solution Approach 2:
The multiple emissive layers are designed to work together as an integrated system where each layer serves multiple functions: exciton formation, energy transfer, and light emission. This multi-functionality reduces the need for additional separate components, simplifying the overall manufacturing process despite the increased layer count
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 results in significantly higher external quantum efficiency and power efficiency, achieving up to 100% internal quantum efficiency and improved stability, especially at high brightness levels required for interior illumination applications, by distributing exciton formation across multiple regions within the OLED structure.
Implementation Method 1
OLEDs make use of thin organic films that emit light when voltage is applied across the device
Data Source
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AI summary
An organic light emitting device having multiple separate emissive layers (420, 430, 440) is provided. Each emissive layer may define an exciton formation region, allowing exciton formation to occur across the entire emissive region. By aligning the energy levels of each emissive layer with the adjacent emissive layers, exciton formation in each layer may be improved. Devices incorporating multiple emissive layers with multiple exciton formation regions may exhibit improved performance, including internal quantum efficiencies of up to 100%.