OLED Lifetime Enhancement Layer for Hole Diffusion Blocking
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Solution Overview
Problem
Existing organic electroluminescent devices face challenges in achieving high efficiency, low voltage, and long lifetime, particularly in blue phosphorescent devices, due to issues with hole diffusion and recombination, which affect color purity and durability.
Innovation Solution
Incorporation of a lifetime enhancement layer (LEL) composed of a bipolar compound with specific electron withdrawal and donor groups, which prevents hole diffusion and enhances electron injection, thereby improving the device's stability and lifetime.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a multilayer-laminated structure is used to improve device performance and efficiency, then light emitting efficiency and lifetime are improved, but device complexity increases
Solution Approach 1:
The device is divided into multiple functional layers including hole injection layer, hole transporting layer, light emitting layer, electron transporting layer, and electron injection layer. Each layer is segmented to perform specific functions, improving overall device performance and lifetime through specialized functionality in each layer.
Solution Approach 2:
The organic material layers are designed to perform multiple functions: charge injection, charge transport, and light emission. This multi-functionality allows a single layer structure to address multiple performance requirements simultaneously, balancing complexity with improved reliability.
2Measurement precision
If high resolution is implemented by forming a larger number of pixels in the same area, then display resolution is improved, but light emitting area decreases and lifetime reduces
Solution Approach 1:
The patent optimizes parameters such as layer thickness, material composition, and energy levels to improve device efficiency. By changing these parameters, the device achieves higher efficiency at reduced current densities, which extends lifetime even when pixel density increases and individual pixel area decreases.
Solution Approach 2:
The multilayer structure ensures continuous and efficient charge transport and recombination across all layers. This continuity maintains high light emitting efficiency even when the total light emitting area is reduced due to higher pixel density, thereby preserving device lifetime.
3Use of energy by moving object
If phosphorescent dopant with heavy atoms is used to improve light emitting efficiency, then internal quantum efficiency increases up to 4 times, but device complexity and material cost increase
Solution Approach 1:
The patent uses composite material systems combining organic host materials with phosphorescent dopants containing heavy atoms like Ir or Pt. This composite approach enables exploitation of phosphorescence to achieve up to 4 times higher internal quantum efficiency compared to fluorescent devices, despite the increased material complexity.
Solution Approach 2:
By adjusting the composition ratio of host to dopant, and optimizing the energy levels of the composite material system, the device achieves high light emitting efficiency. The parameter optimization allows efficient triplet exciton utilization while managing the complexity introduced by phosphorescent materials.
4Illumination intensity
If current density is increased to improve brightness, then illumination intensity is improved, but device lifetime decreases due to accelerated degradation
Solution Approach 1:
The patent optimizes multiple parameters including layer thickness, material energy levels, and composition to maximize light emitting efficiency. By improving efficiency, the device can achieve the same brightness at lower current densities, which reduces stress on the organic materials and extends device lifetime.
Solution Approach 2:
The multilayer structure ensures continuous and balanced charge transport, preventing charge accumulation and reducing localized stress. This continuous operation at optimized current densities maintains high brightness while minimizing degradation mechanisms, thereby extending device 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
The use of a bipolar compound in the LEL layer improves the efficiency and extends the lifetime of the organic electroluminescent device by maintaining exciton formation within the light emitting layer and preventing irreversible decomposition.
Implementation Method 1
the lifetime enhancement layer (LEL) includes a bipolar compound having both an electron withdrawal group (EWG) with a high electron absorption property and an electron donor group (EDG) with a high electron donor property
Implementation Method 2
holes are injected into an organic material layer at the anode, and electrons are injected into an organic material layer at the cathode. When the injected holes and electrons meet each other, an exciton is formed
Implementation Method 3
When the injected holes and electrons meet each other, an exciton is formed, and the exciton falls down to a bottom state to emit light
Data Source
AI summary
The present disclosure provides an organic electroluminescent device including: an anode; a cathode; and one or more organic material layers interposed between the anode and cathode and selected from the group consisting of a hole injection layer, a hole transporting layer, a light emitting layer, an electron transporting layer, and an electron injection layer, and further including a lifetime enhancement layer (LEL) between the light emitting layer and the electron transporting layer.