OLED Control Layer Refractive Index Optimization
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Solution Overview
Problem
The light coupling efficiency of organic light-emitting display devices, particularly the top emission type, is limited by the refractive index mismatch between layers and the low work function of the cathode material, which restricts the brightness and efficiency of the device.
Innovation Solution
Incorporating a control layer with a refractive index lower than adjacent layers, formed from organic materials, between the hole injection and hole transport layers, or within them, to enhance light coupling efficiency by optimizing the refractive index and maximizing the optical resonance effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a transparent cathode with low work function is used in top emission type OLED, then the device can achieve higher aperture ratio and potential light emission efficiency, but the light coupling efficiency is limited due to refractive index mismatch between layers
Solution Approach 1:
The patent introduces a control layer with intermediate refractive index between the hole injection layer and hole transport layer. This intermediary layer acts as a refractive index bridge, gradually transitioning the optical impedance between layers with different refractive indices, thereby reducing light reflection and improving light coupling efficiency in top emission type OLEDs with transparent cathodes
Solution Approach 2:
The patent optimizes the refractive index parameter of the control layer to be intermediate between adjacent layers. By carefully selecting and adjusting the refractive index of the control layer material, the patent achieves optimal light coupling efficiency while maintaining the benefits of transparent cathode structure in top emission type OLEDs
2Loss of energy
If the control layer is positioned within the hole injection layer or between hole injection and hole transport layers, then light coupling efficiency is maximized, but the device structure becomes more complex
Solution Approach 1:
The patent applies the control layer with specific refractive index properties only at the critical interface region between hole injection layer and hole transport layer, where refractive index mismatch causes maximum light reflection. This localized application of special optical properties minimizes the impact on overall device complexity while achieving significant improvement in light coupling efficiency
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 light coupling efficiency and brightness of the organic light-emitting display device by maximizing the resonance effect, even with a transparent cathode having a low work function, thereby overcoming the limitations of existing technologies.
Implementation Method 1
the control layer including an organic material and having a refractive index lower than that of an adjacent layer
Implementation Method 2
the first electrode including a reflection film, the second electrode including a semi-transmissive reflective material
Data Source
AI summary
An organic light-emitting display device includes a substrate, a first electrode on the substrate, the first electrode including a reflection film, a hole injection layer on the first electrode, a hole transport layer on the hole injection layer, an emission layer on the hole transport layer, an electron injection transport layer on the emission layer, a second electrode on the electron injection transport layer, the second electrode including a semi-transmissive reflective material, and a control layer positioned between a lower surface of the hole injection layer and an upper surface of the hole transport layer, the control layer including an organic material and having a refractive index lower than that of an adjacent layer.