OLED Anti-Reflective Dielectric Layer for Light Extraction
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Solution Overview
Problem
Organic light-emitting diodes (OLEDs) face challenges in achieving optimal light emission efficiency and contrast in ambient light due to reflection from the opaque current-distributing sublayer, which degrades emission contrast and luminous efficiency.
Innovation Solution
A top-emitting OLED structure with a transparent conducting sublayer and an opaque current-distributing metal sublayer, combined with a dielectric antireflection layer of uniform thickness, is used to minimize reflectance at ambient light wavelengths, enhancing emission contrast and luminous efficiency by optimizing the antireflection and semireflective properties of the upper electrode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an opaque current-distributing metal sublayer is used in the upper electrode, then current distribution is improved, but light emission contrast is degraded due to reflection
Solution Approach 1:
A transparent dielectric antireflection layer is introduced as an intermediary between the opaque metal sublayer and the external environment. This layer mediates the interaction between ambient light and the metal grid, reducing harmful reflections while allowing the metal to maintain its current-distributing function. The antireflection layer has optical properties that minimize reflectance at the metal-dielectric interface, thereby improving emission contrast without compromising current distribution.
2Illumination intensity
If a transparent dielectric antireflection layer is applied over the entire active surface, then reflectance of ambient light is reduced, but overall transparency of the upper electrode is degraded
Solution Approach 1:
The antireflection function is localized to where it is most needed - above the opaque metal sublayer where ambient light reflection occurs. The transparent dielectric layer is positioned specifically to cover the metal grid structure, providing antireflection properties only in the zones where the metal is present. This localized approach maintains high transparency in the light-emitting regions while effectively reducing reflectance over the metal portions.
3Loss of energy
If the transparent conducting sublayer is made thinner to improve transparency, then light extraction is improved, but electrical conductivity is reduced
Solution Approach 1:
The electrical conductivity function is merged between two components: the transparent conducting sublayer and the opaque metal sublayer. The transparent conducting sublayer provides baseline conductivity and charge injection, while the opaque metal sublayer provides enhanced current distribution. Together, they form a hybrid conductive system that achieves both good electrical performance and optical transparency, with each layer compensating for the limitations of the other.
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 solution significantly improves light extraction and luminous efficiency by reducing ambient light reflectance and optimizing the optical properties of the upper electrode, resulting in enhanced emission contrast and light extraction through the use of a dielectric antireflection layer and a semireflective upper layer.
Implementation Method 1
a transparent dielectric antireflection layer of approximately uniform thickness is in contact, via its external face, with a medium, generally air, and, in contact via its internal face, with the transparent conducting sublayer and the opaque metal sublayer
Implementation Method 2
The material and the thickness of the dielectric antireflection layer are chosen with the material of the current-distributing metal sublayer so that the reflectance of the opaque zones, measured at normal incidence at a wavelength λamb close to 550 nm, is less than 0.1
Implementation Method 3
an organic electroluminescent layer capable of emitting light, interposed between a lower electrode and a partially transparent upper electrode, which are designed to pass a current through the organic electroluminescent layer and thus cause, within this layer, the emission of light
Data Source
AI summary
The diode comprises an organic electroluminescent layer interposed between a lower electrode and a partially transparent and semireflective upper electrode, which itself comprises a transparent conducting sublayer and a current-distributing metal sublayer, for example an opaque grid. A dielectric antireflection layer is deposited on the grid to improve the emission contrast in ambient light, which grid, according to an advantageous embodiment, is designed to optimize the semireflective properties of the upper electrode, thereby improving, by an optical cavity effect, extraction of the emitted light.