High-Index Performance Enhancement Layer for OLED Light Extraction
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Solution Overview
Problem
Organic light-emitting diode (OLED) devices face inefficiencies in light extraction due to internal reflection and are prone to shorting defects, which reduce their luminous output and display quality, and existing solutions either increase complexity or do not effectively address pinhole and structural issues.
Innovation Solution
Incorporating a high-index performance enhancement layer (PEL) between the electrodes, with a thickness of at least 20 nm and an optical index at least 0.1 higher than the transparent electrode, to enhance light emission efficiency and reduce shorting defects by introducing new reflecting interfaces and reducing electrical resistivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a typical OLED device structure with glass substrate, transparent conducting anode, organic layers, and reflective cathode is used, then light can be emitted through the glass substrate, but nearly 60% of generated light is trapped by internal reflection in the ITO/organic EL element and 20% is trapped in the glass substrate, resulting in only about 20% light extraction efficiency
Solution Approach 1:
The patent introduces a performance enhancement layer (PEL) with high refractive index (at least 0.1 higher than the transparent electrode) as an intermediary component between the transparent electrode and the organic light-emitting element. This PEL layer acts as an optical mediator that reduces total internal reflection at the interfaces by providing a gradual refractive index transition, thereby extracting trapped photons and improving light extraction efficiency from approximately 20% to significantly higher levels while maintaining device structure integrity
Solution Approach 2:
The patent modifies the optical parameters of the device structure by incorporating a PEL layer with specifically controlled refractive index (at least 0.1 higher than the transparent electrode) and thickness (at least 20 nm). This parameter change in the refractive index profile at the electrode-organic layer interface fundamentally alters the light propagation characteristics, reducing internal reflection losses and enhancing light extraction without requiring complex structural modifications
2Length of moving object
If the separation between anode and cathode is reduced to improve device compactness, then device size is minimized, but the devices become prone to shorting defects due to pinholes, cracks, and roughness
Solution Approach 1:
The performance enhancement layer serves as an intermediary barrier layer between the transparent conducting anode and the organic light-emitting element. This PEL layer with its specific optical and electrical properties acts as a protective mediator that prevents direct contact between the anode and organic layers, thereby blocking shorting pathways caused by pinholes, cracks, or surface roughness while maintaining the reduced device thickness required for compact applications
Solution Approach 2:
The patent incorporates the PEL layer in advance during device fabrication, before the organic light-emitting element is fully assembled. This PEL layer provides beforehand cushioning or protection against potential shorting defects by creating a buffer zone that compensates for surface imperfections and prevents direct electrical contact between the anode and cathode, thereby enhancing device reliability before operational stresses occur
3Illumination intensity
If existing solutions such as micro-lens arrays, corrugated substrates, or special micro-structures are added to enhance light extraction, then light extraction efficiency is improved, but device construction complexity is much increased
Solution Approach 1:
The patent merges the light extraction enhancement function directly into the existing device structure by incorporating the performance enhancement layer as an integral component between the transparent electrode and the organic light-emitting element. This merging approach combines the optical enhancement function with the existing electrode and organic layer structure, avoiding the need for separate added components like micro-lens arrays or corrugated substrates, thereby improving light extraction while maintaining simple device construction
Solution Approach 2:
The performance enhancement layer serves multiple functions simultaneously: it enhances light extraction efficiency through its high refractive index, provides electrical isolation to prevent shorting defects, and maintains compatibility with standard OLED fabrication processes. This multi-functionality eliminates the need for separate specialized components, achieving improved light extraction without increasing device construction complexity
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 PEL significantly enhances light output efficiency, reduces susceptibility to shorting defects, and allows for lower drive voltages while maintaining improved angular and wavelength independence, making it suitable for practical applications.
Implementation Method 1
Due to the high optical indices of the organic materials used, most of the photons generated by the recombination process are actually trapped in the devices due to total internal reflection
Implementation Method 2
Incorporating a high-index performance enhancement layer (PEL) between the electrodes, with a thickness of at least 20 nm and an optical index at least 0.1 higher than the transparent electrode, to enhance light emission efficiency by introducing new reflecting interfaces
Implementation Method 3
Light is generated in an OLED device when electrons and holes that are injected from the cathode and anode, respectively, flow through the electron-transporting layer and the hole-transporting layer and recombine in the light-emitting layer
Data Source
AI summary
An organic light-emitting device includes a substrate; a first electrode and a second electrode positioned relative to the substrate in which at least one of the electrodes is the transparent electrode; an organic light-emitting element including at least a light-emitting layer disposed between the two electrodes; and a performance enhancement layer disposed between the two electrodes; wherein the performance enhancement layer is high index and has a thickness of at least 20 nm.