OLED Light Extraction via Scattering Layer and Low-Index Element
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Solution Overview
Problem
OLED devices suffer from inefficiencies in light output due to internal reflection and environmental degradation, with existing solutions failing to effectively extract trapped light and provide adequate protection against moisture, leading to reduced efficiency and lifespan.
Innovation Solution
An OLED device structure featuring a transparent encapsulating layer, a scattering layer between the encapsulating layers, and a low-index element between the encapsulating layer and the transparent cover, which enhances light extraction and environmental protection by scattering trapped light and preventing moisture ingress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional OLED structure with high refractive index materials (ITO, organic layers, glass) is used, then device simplicity is maintained, but light extraction efficiency deteriorates with up to 80% of light trapped by internal reflection
Solution Approach 1:
A scattering layer is introduced as an intermediary component between the OLED element and the encapsulating layers. This scattering layer mediates the interaction between trapped light and the device structure, redirecting light paths to enable extraction of previously trapped photons without complicating the fundamental device architecture
Solution Approach 2:
The optical parameters of the device structure are modified by introducing materials with different refractive indices and scattering properties. The scattering layer changes the light propagation parameters, reducing total internal reflection and improving light extraction efficiency while maintaining structural simplicity
2Reliability
If encapsulating layers are added to protect against moisture, then environmental protection is improved, but light extraction efficiency deteriorates due to additional high refractive index layers trapping more light
Solution Approach 1:
The scattering layer serves as a mediator positioned between the OLED element and encapsulating layers. It intercepts light before it enters the encapsulating layers, scattering trapped light at angles that enable extraction through the encapsulation structure, thus protecting moisture sensitivity while improving light output
Solution Approach 2:
The scattering layer introduces a new dimensional aspect to light management by scattering light in multiple directions rather than allowing straight-line propagation. This dimensional change in light paths enables extraction through the encapsulating layers that would otherwise trap light
3Illumination intensity
If light is emitted in all directions from internal layers, then complete light coverage is achieved, but light extraction efficiency deteriorates as most light is trapped by total internal reflection and never leaves the device
Solution Approach 1:
The scattering layer acts as an intermediary that intercepts omnidirectionally emitted light and redirects it. By scattering light at various angles, it converts isotropic emission into anisotropic extraction paths, enabling more light to escape the device while maintaining complete angular coverage of the emission
Solution Approach 2:
The high refractive index materials that cause total internal reflection and trap light are converted from harmful to beneficial by using the scattering layer to exploit the trapped light. Instead of losing trapped light, the scattering layer redirects it to extraction angles, converting the previously harmful trapping effect into beneficial light output enhancement
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 increases light output, improves sharpness, and extends the device's lifetime by effectively extracting trapped light and maintaining a low moisture permeation rate, thereby enhancing the overall performance of OLED devices.
Implementation Method 1
a scattering layer between the encapsulating layers, which enhances light extraction and environmental protection by scattering trapped light
Implementation Method 2
a low-index element between the encapsulating layer and the transparent cover, which enhances light extraction and environmental protection
Data Source
AI summary
An organic light-emitting diode (OLED) device, comprising: one or more OLED elements including first and second spaced-apart electrodes with one or more organic layers formed there-between, at least one organic layer being a light-emitting layer, wherein at least one of the electrodes is a transparent electrode, and wherein the light-emitting layer has a first refractive index; a first transparent encapsulating layer formed over the transparent electrode opposite the organic layer; a scattering layer formed over the first encapsulating layer opposite the transparent electrode; a second encapsulating layer formed over the scattering layer opposite the first transparent encapsulating layer; a transparent cover through which light is emitted having a second refractive index; and a low-index element having a refractive index lower than the first and second refractive indices formed between the second encapsulating layer and the transparent cover.