OLED Multi-Emissive Layer Exciton Confinement
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Solution Overview
Problem
Current organic light emitting diodes (OLEDs) face inefficiencies in emission and absorption, poor processing ability, and stability issues due to the limitations of existing materials used in emissive layers.
Innovation Solution
The implementation of a multi-emissive material layer (EML) structure with a doped electron blocking layer (EBL) in OLEDs, where the emitter concentration in each layer is optimized to confine excitons and alleviate charge imbalance, enhancing device efficiency and operational lifetime.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single emissive material layer is used in OLEDs, then the device structure is simple, but the emission efficiency and absorption efficiency are poor
Solution Approach 1:
The emissive layer is segmented into multiple sub-layers (first emissive sub-layer, second emissive sub-layer, and third emissive sub-layer), each with different emitter concentrations. This segmentation allows optimization of emission efficiency in each sub-layer while maintaining overall device performance, resolving the contradiction between structural simplicity and emission efficiency.
Solution Approach 2:
Different regions of the emissive layer are assigned different emitter concentrations to optimize local emission properties. The first sub-layer has higher emitter concentration for strong emission, while subsequent layers have progressively lower concentrations to reduce quenching effects, achieving local optimization of emission efficiency throughout the layer.
2Device complexity
If existing materials are used in emissive layers, then the device structure is straightforward, but the processing ability and stability are poor
Solution Approach 1:
The patent employs composite material systems where multiple emitters with different concentrations are combined within a single emissive layer structure. This composite approach enhances device stability and processing ability by distributing stress and energy across multiple material components rather than relying on a single material system.
3Illumination intensity
If high emitter concentration is used in the emissive layer, then the emission intensity is high, but exciton quenching increases and reduces operational lifetime
Solution Approach 1:
The emissive layer is divided into multiple sub-layers with different emitter concentrations. The first sub-layer uses high emitter concentration to achieve strong emission intensity, while subsequent sub-layers use progressively lower concentrations to minimize exciton quenching effects, thereby extending operational lifetime while maintaining overall emission intensity.
Solution Approach 2:
Different emitter concentrations are applied locally within different sub-layers of the emissive layer. This local quality variation allows high emission intensity in regions where it is most needed while reducing exciton quenching in other regions, optimizing the balance between emission intensity and operational lifetime.
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 configuration improves the external quantum efficiency, power efficiency, and extends the operational lifetime of OLEDs by confining electron and hole recombination within the emissive layer, reducing exciton quenching and charge buildup, leading to more stable and efficient device performance.
Implementation Method 1
the concentration of the first emitter in the first EML (hole favorable) exceeds that of the second emitter in the second EML (electron favorable)... confining excitons and alleviating charge imbalance
Implementation Method 2
organic light emitting devices with a multi-emissive material layer (EML)... compounds capable of absorbing and/or emitting light
Data Source
AI summary
The present invention relates to organic light emitting devices with a multi-emissive material layer (EML), where a multi-EML generally refers to an emissive layer having at least two layers of emissive material, each layer having a different emitter concentration (e.g. a first EML in direct contact with a second EML, and the emitter concentration of the first EML (hole favorable) exceeds that of the second EML (electron favorable)).