Substrate Scattering Layer for OLED Light Extraction
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Solution Overview
Problem
Conventional organic electronic devices (OEDs) face challenges in achieving high light output due to light being trapped at the interface between the organic layer and the substrate, resulting in low light extraction efficiency, primarily because of the mismatch in refractive indices between the organic layer and the substrate.
Innovation Solution
A substrate for OEDs is designed with a base layer and a scattering layer, where the scattering layer is formed using a binder with a refractive index of 1.7 or more, combined with scattering particles of varying refractive indices, to enhance light extraction efficiency. The substrate also includes a planarized layer to provide a smooth surface for the OED, and an electrode layer is formed on top to further improve light extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional substrate with glass base layer is used, then the device structure is simple and easy to manufacture, but light extraction efficiency is low due to refractive index mismatch
Solution Approach 1:
The substrate is constructed as a composite material system consisting of a glass base layer and a polymer scattering layer. The scattering layer contains scattering particles (such as TiO2, SiO2, or ZrO2) dispersed in a polymer binder, creating a multi-phase composite structure that combines the mechanical stability of glass with the optical scattering properties of the polymer-scatterer composite.
Solution Approach 2:
The scattering layer is applied locally on the inner surface of the glass substrate, creating a region with different optical properties (higher scattering coefficient) only where light extraction enhancement is needed. This localized modification preserves the overall simplicity of the substrate while addressing the specific light trapping problem at the organic layer-substrate interface.
2Loss of energy
If a scattering layer with high refractive index binder is used, then light extraction efficiency is improved, but the device structure becomes more complex
Solution Approach 1:
The scattering layer integrates multiple functions into a single component: it provides optical scattering to enhance light extraction, adheres to the glass substrate through binder properties, and can be applied as a thin conformal coating. By combining scattering particles, binder, and adhesion functions in one layer, the design avoids adding separate complex subsystems.
Solution Approach 2:
The refractive index of the scattering layer is optimized by selecting binder materials and scattering particle compositions that provide the desired optical contrast. The scattering layer's refractive index is tuned to be between 1.7 and 2.0, creating optimal contrast with the organic emitting layer (refractive index ~1.8) while maintaining practical manufacturability.
3Loss of energy
If the scattering layer is made with high refractive index material, then light extraction efficiency is enhanced, but moisture and gas barrier properties may be compromised
Solution Approach 1:
The scattering layer is designed as a thin film coating on the inner surface of the glass substrate. The glass substrate itself serves as the primary barrier layer against moisture and gas penetration, while the thin scattering layer provides optical functionality without significantly compromising the barrier properties of the overall substrate structure.
Solution Approach 2:
The scattering layer uses a composite formulation with polymer binder and inorganic scattering particles. The polymer matrix provides continuity and adhesion, while the inorganic particles provide scattering. The overall substrate system (glass + scattering layer) maintains barrier properties because the glass substrate forms the dominant barrier, and the scattering layer can be designed with low porosity to minimize additional permeation pathways.
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 substrate significantly enhances light extraction efficiency, as demonstrated by a 54% external quantum efficiency in an OLED example, while also preventing moisture and gas penetration from the external environment, resulting in improved performance and durability of the OED.
Implementation Method 1
a scattering layer, wherein the scattering layer is formed on the base layer
Implementation Method 2
the light generated in the organic emitting layer in the bottom emitting device is trapped at an interface between the organic layer and the first electrode layer or in the substrate due to a total internal reflection phenomenon
Data Source
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AI summary
Provided are a substrate for an organic electronic device (OED), an OED, and lighting. The substrate capable of forming an OED may have excellent performances including light extraction efficiency and prevent penetration of moisture or a gas from an external environment, and thus an OED having excellent performance and durability may be provided.