Diffraction Grating Waveguide for Organic EL Light Extraction
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Solution Overview
Problem
Organic EL displays suffer from low luminous efficiency due to insufficient outcoupling efficiency of light emitting elements, with a significant portion of emitted light being totally reflected at the front electrode interface, limiting the display's ability to output light effectively.
Innovation Solution
Incorporation of a diffraction grating with a specifically defined grating constant in the optical device, which causes first-order diffracted light to emerge from the light-emitting element or waveguide layers, enhancing the directivity and reducing total reflection of light at the interface between the light transmitting insulating layer and the exterior.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If light is emitted from the organic EL element, then the display can show images, but a great portion of the light is totally reflected at the front electrode interface and cannot exit the element
Solution Approach 1:
A light extracting structure (diffraction grating or microlens array) is introduced as an intermediary component between the organic EL element and the external environment. This structure acts as a mediator that redirects light paths, enabling light that would otherwise be totally reflected to exit the display at angles within the escape cone, thereby converting reflection loss into useful light output.
Solution Approach 2:
The optical parameters of the light extracting structure (such as grating period, depth, or lens focal length) are optimized to match the emission characteristics of the organic EL element. By adjusting these parameters, the structure effectively redirects light at specific angles that fall within the escape cone, transforming the directional distribution of emitted light to maximize extraction efficiency.
2Use of energy by moving object
If a diffraction grating is added to improve light extraction, then luminous efficiency increases, but device complexity increases
Solution Approach 1:
The light extracting structure serves multiple functions simultaneously: it acts as a diffraction grating to redirect light, provides structural support for the display layers, and can be integrated with the electrode pattern or encapsulation layers. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in device complexity while achieving improved light extraction.
Solution Approach 2:
The light extracting structure is merged with existing display components rather than being added as a completely separate element. For example, the diffraction grating pattern can be formed directly on the front electrode or encapsulation layer during the same fabrication process, combining the optical extraction function with the structural and electrical functions of these layers.
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 significantly enhances the luminous efficiency of the organic EL display by ensuring that a greater portion of emitted light is outputted with high directivity, overcoming the limitations of total reflection and improving the display's brightness and viewing angle.
Implementation Method 1
a diffraction grating which is disposed on a back side of the second waveguide layer and faces the first waveguide layer, wherein a grating constant of the diffraction grating is defined such that a first-order diffracted light emerges from the second waveguide layer
Implementation Method 2
a light component having a highest intensity of light which propagates in an in-plane direction while causing multiple reflection in the first waveguide layer
Data Source
AI summary
An optical device includes a first waveguide layer in which multiple-beam interference occurs, a second waveguide layer which includes a back surface facing the first waveguide layer and a front surface as a light output surface, and a diffraction grating which is arranged on a back side of the second waveguide layer and faces the first waveguide layer, wherein a grating constant of the diffraction grating is defined such that a first-order diffracted light emerges from the second waveguide layer, the first-order diffracted light being generated when a light component having a highest intensity of light which propagates in an in-plane direction while causing multiple reflection in the first waveguide layer enters the diffraction grating.