Organic Light Emitting Device With Gradient Hole Transport Layers
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Solution Overview
Problem
Organic light emitting devices face limitations in emission efficiency and lifespan due to high driving voltage and properties of organic materials, particularly in blue emission layers using fluorescent materials, which result in inefficient light coupling and shortened device lifespan.
Innovation Solution
The organic light emitting device incorporates multiple emission layers with complementary colors and hole transport layers of varying mobilities, including a mixed host and dopant system, to enhance hole and electron coupling and prevent electron transfer, thereby improving emission efficiency and lifespan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple emission layers with complementary colors are used to improve color realization and emission efficiency, then the device structure becomes more complex
Solution Approach 1:
The emission layer is segmented into multiple sub-layers (first emission layer, second emission layer, third emission layer) with different color emissions. Each layer contains specific host and dopant materials optimized for its color range, allowing independent optimization of each layer's emission characteristics while maintaining overall device efficiency
Solution Approach 2:
Each emission layer uses composite material systems with specific host-dopant combinations. The first emission layer uses host material 1 with dopant material 1 for blue-green emission, the second emission layer uses host material 2 with dopant material 2 for yellow-green emission, and the third emission layer uses host material 3 with dopant material 3 for red emission, creating a composite structure that achieves high color purity and efficiency
2Reliability
If hole transport layers with varying mobilities are introduced to improve hole-electron coupling, then the manufacturing process becomes more complex
Solution Approach 1:
Different hole transport layers are positioned at specific locations within the device structure with locally optimized properties. The first hole transport layer is located between the first emission layer and second emission layer with mobility optimized for that interface, while the second hole transport layer is positioned between the second emission layer and third emission layer with different mobility characteristics suited for that region
Solution Approach 2:
The hole mobility parameter is systematically varied across different hole transport layers. The first hole transport layer has a mobility in the range of 10^-6 to 10^-8 cm²/Vs, while the second hole transport layer has a mobility in the range of 10^-8 to 10^-10 cm²/Vs, creating a gradient that optimizes charge transport and coupling efficiency at different depths of the device
3Device complexity
If fluorescent materials are used in blue emission layers to simplify the device structure, then the emission efficiency and lifespan are reduced
Solution Approach 1:
The blue emission layer uses a composite material system consisting of host material 1 and dopant material 1 with specific molecular structures and energy level alignments. This composite approach enables efficient exciton generation and radiative decay, achieving both high emission efficiency and extended operational lifespan while maintaining the relatively simple fluorescent material-based device structure
4Power
If electron and hole injection layers are added to lower driving voltage, then the device complexity increases and may cause electron overflow to hole injection layer
Solution Approach 1:
Hole transport layers serve as intermediary structures between the emission layers and the electrodes. These intermediary layers with carefully controlled mobility values act as buffers that facilitate hole injection from the anode while preventing electron overflow into the hole injection layer, thereby maintaining proper charge separation and reducing the required driving voltage without causing harmful charge mixing
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 significantly enhances emission efficiency by up to 10% and extends the lifespan of blue emission layers, achieving higher performance compared to traditional designs.
Implementation Method 1
when an electron generated in the cathode and a hole generated in the anode are injected into the inside of the emission layer, exciton is produced by the injected electron and hole, to thereby generate light
Implementation Method 2
the phenomenon of phosphorescence indicates that a light emission persists for a long time even after a removal of an external stimulus applied to a certain object, and the phenomenon of fluorescence indicates a light emission is stopped immediately after a removal of an external stimulus applied to a certain object
Implementation Method 3
in case of the fluorescent material, an electron firstly becomes an excited state, and then directly becomes a ground state, whereby the emission time period of the fluorescent material is relatively shorter than the emission time period of the phosphorescent material
Data Source
AI summary
An organic light emitting device includes a first emitting part on an anode, the first emitting part including a first emission layer and a first hole transport layer a second emitting part on the first emitting part, the second emitting part including a second emission layer and a second hole transport layer; a third emitting part on the second emitting part including a third emission layer and a third hole transport layer; and a cathode on the third emitting part. The third emitting part further includes a fourth emission layer to emit light having a same color as the third emission layer and includes a dopant and a mixed host of at least two hosts, and a fourth hole transport layer provided on the third hole transport layer while in contact with the third emission layer, and has a hole mobility lower than that of the third hole transport layer.