Reflective Cavity Electrode for QLED Light Extraction
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Solution Overview
Problem
Conventional light-emitting devices, such as QLED and OLED, face significant light loss due to total internal reflection (TIR) in high refractive index filler encapsulation layers, which existing methods have not effectively addressed by modifying the optical cavity structure.
Innovation Solution
The implementation of a reflective optical cavity structure along the bank structure, utilizing multiple conductive layers separated by a non-conductive dielectric layer, to out-couple light trapped by TIR, with the conductive layers extending along the inner surface of the bank structure facing the filler material layer, allowing for controlled shape and thickness to maximize light extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a thick top filler layer with high refractive index is used to reduce Fresnel reflections and increase transmissivity, then light transmission through the top electrode is improved, but light is trapped by total internal reflection (TIR) at the interface with lower refractive index materials
Solution Approach 1:
The patent converts the harmful effect of TIR-trapped light into a beneficial resource by introducing a reflective bank structure. The reflective bank captures light that would otherwise be trapped by TIR at the filler layer interface and redirects it back into the emissive cavity, transforming energy loss into useful light output. This resolves the contradiction by maintaining high transmissivity while recovering otherwise lost light through the reflective structure.
Solution Approach 2:
The reflective bank structure acts as an intermediary element between the filler layer and the surrounding environment. It mediates the interaction by capturing TIR-trapped light and redirecting it back into the cavity, serving as a bridge that converts trapped light into extractable light without altering the filler layer's high refractive index properties that enable low Fresnel reflection.
2Loss of energy
If reflective and/or scattering bank structures are used to out-couple light trapped by TIR, then light extraction is improved, but the device complexity increases
Solution Approach 1:
The reflective bank structure serves multiple functions simultaneously: it acts as a reflective surface to out-couple TIR-trapped light, provides structural definition for the pixel region, and can be integrated with the electrode pattern. This multi-functionality reduces the need for separate components, thereby managing device complexity while achieving improved light extraction.
Solution Approach 2:
The patent merges the reflective bank structure with the existing electrode pattern and pixel definition structures. By combining multiple functions into a single integrated structure, the complexity increase is minimized while still achieving the light extraction benefit. The reflective bank is formed as part of the standard fabrication process rather than as an add-on component.
3Use of energy by moving object
If the reflective optical cavity thickness is increased to reduce capacitance, then electrical performance is improved, but the structural complexity and manufacturing precision requirements increase
Solution Approach 1:
The patent optimizes the reflective optical cavity thickness as a design parameter to achieve the desired balance between capacitance reduction and manufacturing feasibility. By carefully selecting the thickness within a specific range, the design achieves sufficient capacitance reduction for electrical performance while remaining within the capabilities of standard manufacturing processes, thus resolving the contradiction between electrical optimization and manufacturing precision.
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 enhances light extraction from the emissive cavity, increasing overall light output and tolerance in design, reducing light trapped by TIR and improving on-axis brightness and efficiency.
Implementation Method 1
Light traveling through the high refractive index layer, however, largely will be trapped by total internal reflection (TIR). TIR happens when light that propagates in a first dielectric meets an interface with a second dielectric of lower refractive index at such an angle to the normal to the interface that no propagation in the second dielectric is possible from the laws of electromagnetism (Snell's Law).
Implementation Method 2
One alternative to modifying the cavity is to use a thick top 'filler' layer with a relatively high refractive index, which enables Fresnel reflections to be reduced and transmissivity through a top electrode to be increased.
Data Source
AI summary
A light-emitting device has enhanced light output by employing a reflective optical cavity along the bank structure to improve light extraction. The light-emitting device includes a bank structure; an emissive cavity disposed within the bank structure; a filler material layer disposed within the bank structure and on a light-emitting side of the emissive cavity; and a reflective optical cavity disposed along an inner surface of the bank structure facing the filler material layer. The reflective optical cavity is configured to out-couple light that is internally reflected by an emitting side surface of the filler material layer and is incident on the reflective optical cavity. The reflective optical cavity incudes a first conductive layer and a second conductive layer that are separated by a non-conductive dielectric layer. The first conductive layer is disposed against the inner surface of the bank structure, and the second conductive layer is disposed against the filler material layer opposite from the inner surface of the bank structure. The emissive cavity includes an emissive layer disposed between a first electrode layer and a second electrode layer, and the first conductive layer may be configured as an extension of the first electrode layer and the second conductive layer may be configured as an extension of the second electrode layer.