Concave Reflective Layer for Organic EL Light Extraction
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Solution Overview
Problem
Organic electroluminescence (EL) devices suffer from low light use efficiency due to a significant portion of emitted light being confined within the light emitting layer, rather than being extracted externally, which limits their performance in both display and illumination applications.
Innovation Solution
The organic EL device incorporates a base material with a first recess and a reflective layer, a filling layer with light transmissivity, and electrodes with light transmissivity and reflectivity, where the light emitting area is positioned inside a second recess, and the reflective layer is in contact with the first electrode, forming a concave reflective surface with a focus area within the light emitting area. This configuration enhances light extraction by reflecting light at the concave surface and focusing it for external emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a planar reflective layer is used in conventional organic EL devices, then the device structure is simple, but light use efficiency is low due to total internal reflection confining most light inside the light emitting layer
Solution Approach 1:
The reflective layer is formed with a concave curved surface instead of a planar surface. The curvature radius is specifically designed to be 0.5 mm to 5 mm to optimize light reflection and extraction. This curved geometry enables light emitted from the light emitting layer to be reflected at appropriate angles, escaping the total internal reflection constraint and significantly improving light use efficiency.
Solution Approach 2:
The concave reflective surface creates different local reflection characteristics across the device area. Light rays at different positions and angles experience different reflection paths, with the curved surface specifically designed to redirect confined light toward extraction paths while maintaining appropriate optical properties in different regions of the light emitting layer.
2Loss of energy
If the light emitting area is positioned at the interface between light emitting layer and air, then light extraction is maximized in conventional devices, but image quality degrades due to bleeding and light use efficiency remains low
Solution Approach 1:
The concave reflective surface with curvature radius of 0.5 mm to 5 mm redirects light paths to achieve both high extraction efficiency and sharp image quality. The curved geometry focuses reflected light appropriately, preventing bleeding while maximizing the amount of light extracted from the light emitting layer, thus simultaneously improving light use efficiency and image quality.
Solution Approach 2:
The light emitting area is nested within the concave reflective structure, with the light emitting layer positioned above the curved reflective surface. This nested configuration allows the reflective surface to be contained within the overall device structure while providing enhanced light extraction functionality, improving both image quality and light use efficiency without increasing overall device footprint.
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 design significantly improves light use efficiency, as demonstrated by increased luminance current efficiency compared to conventional organic EL devices, allowing for high luminance with low power consumption across various color light emitting elements.
Implementation Method 1
a reflective layer provided along at least a surface of the first recess... the reflective layer is in contact with the first electrode in a periphery of the first recess
Implementation Method 2
forming a concave reflective surface with a focus area within the light emitting area. This configuration enhances light extraction by reflecting light at the concave surface and focusing it for external emission.
Implementation Method 3
a filling layer filled in the first recess, the filling layer including a top surface on which a second recess is provided, the filling layer having light transmissivity
Data Source
AI summary
An organic EL device according to one aspect of the present invention includes: a base material; a first recess provided on a top surface of the base material; a reflective layer provided along a surface of the first recess; a filling layer filled in the first recess, the filling layer including a top surface on which a second recess is provided; a first electrode provided on an upper layer side of the filling layer; an organic layer comprising a light emitting layer provided on an upper layer side of the first electrode; and a second electrode provided on an upper layer side of the organic layer. Within the organic layer, a part of a light emitting area interposed between the first electrode and the second electrode is positioned inside the second recess The reflective layer is in contact with the first electrode in a periphery of the first recess.