OLED Light Extraction via Refractive Index Bridge

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Solution Overview

Problem

The existing configuration of organic electroluminescence (OLED) display devices has a low light extraction efficiency due to the higher refractive index of the inorganic sealing film compared to the filling layer, causing light emitted obliquely from the organic light-emitting diode to be reflected at the interface between the inorganic sealing film and the filling layer, leading to reduced light extraction efficiency.

Innovation Solution

A display device structure is introduced that includes a substrate with an organic light-emitting diode, an insulating layer, a first refractive index layer with a higher refractive index, and a second refractive index layer with a lower refractive index, where the second refractive index layer is positioned inside a recessed portion of the first refractive index layer, and the first refractive index layer is shaped to conform to the insulating layer, enhancing light extraction by reducing reflections at the interfaces.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If an inorganic sealing film with higher refractive index than the filling layer is used, then the sealing performance and structural integrity are improved, but light extraction efficiency deteriorates due to reflection at the interface

Engineering Contradiction:

Improvesealing performanceVSAvoidlight extraction efficiency

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

A refractive index control layer is introduced as an intermediary between the inorganic sealing film and the filling layer. This layer has a refractive index that is lower than the inorganic sealing film but higher than or equal to the filling layer, serving as a refractive index bridge to reduce reflection and improve light extraction efficiency while maintaining the sealing function of the inorganic film

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The refractive index control layer is selectively formed only in specific regions where light extraction needs to be enhanced, such as above the bank structure or in predetermined patterns, rather than uniformly across the entire display device. This allows local optimization of light extraction without compromising overall sealing performance

Inventive Principle:

Principle #3Local quality

2Ease of manufacture

If a uniform refractive index structure is used, then the manufacturing process is simplified, but light extraction efficiency is reduced due to reflection at interfaces with different refractive indices

Engineering Contradiction:

Improvemanufacturing simplicityVSAvoidlight extraction efficiency

Core Design Contradiction:

Ease of manufactureVSLoss of energy

Solution Approach 1:

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

Instead of modifying the entire sealing structure, the refractive index control layer is applied partially only in regions where it is most needed for light extraction, such as above the banks or in specific pixel regions, achieving sufficient improvement without excessive manufacturing complexity

Inventive Principle:

Principle #16Partial or excessive action

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 extraction efficiency by refracting light emitted obliquely from the organic light-emitting diode, reducing reflections and increasing the amount of light emitted in the front direction, thereby enhancing the visual characteristics and color separation of the display device.

Implementation Method 1

The first refractive index layer is made of a material having a first refractive index, and has a first recessed portion overlapping with a formation region of the insulating layer in plan view. The second refractive index layer is made of a material having a second refractive index lower than the first refractive index.

Methodology Applied

Scientific EffectRefraction: Refraction

Implementation Method 2

when light emitted from the organic light-emitting diode in a direction oblique to a light-emitting surface of the diode is incident on the inorganic sealing film formed above the bank, the light is reflected at an interface between the inorganic sealing film and the filling layer

Methodology Applied

Scientific EffectReflection: Reflection

Data Source

PatentUS10541385B2Display device and method of manufacturing a display device

Publication Date: 2020.01.21 MAGNOLIA WHITE CORP

AI summary

A display device according to an embodiment of the present invention includes: a substrate; an organic light-emitting diode provided for each pixel on the substrate; an insulating layer that is formed along a boundary of the pixel and has an opening portion in a light-emitting region of the pixel; a first refractive index layer; and a second refractive index layer. The first refractive index layer is disposed on the insulating layer and the organic light-emitting diode, is made of a material having a first refractive index, and has a first recessed portion overlapping with a formation region of the insulating layer in plan view. The second refractive index layer is disposed inside the first recessed portion and is made of a material having a second refractive index lower than the first refractive index.