Light Extracting Electrode for OLED Waveguide Loss
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Solution Overview
Problem
Conventional OLED devices suffer from a significant optical waveguide effect, where about 80% of the visible light emitted from the emissive layer is trapped inside the device, resulting in only 20% being emitted, due to reflection at the interfaces of the various layers, leading to reduced light output.
Innovation Solution
A light extracting electrode with a metallic layer incorporating light scattering features, such as dendrites or defects, is introduced to disrupt the waveguide effect, increasing the haze and allowing more electromagnetic radiation to be emitted by scattering light randomly and promoting its exit through the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional OLED device structure is used, then the device structure is simple and easy to manufacture, but about 80% of the visible light emitted from the emissive layer is trapped inside the device due to the optical waveguide effect
Solution Approach 1:
The patent introduces an intermediary layer (microsphere layer or scattering layer) between the encapsulation layer and the emissive layer to mediate light extraction. This intermediary layer contains particles with refractive indices between air and the encapsulation layer, creating gradient refractive index transitions that reduce total internal reflection and enable more light to escape the device without complicating the overall structure
Solution Approach 2:
The patent changes the refractive index parameter by introducing particles with specific refractive indices (1.4-1.6 for microspheres, 1.7-2.0 for scattering layer) into the device structure. This parameter modification creates optimal optical conditions for light extraction by matching refractive indices across interfaces, thereby improving light extraction efficiency while maintaining structural simplicity
2Productivity
If the optical waveguide effect is reduced by adding light scattering layers or microspheres, then light extraction efficiency is improved, but the device complexity increases
Solution Approach 1:
The patent makes the encapsulation layer multi-functional by having it serve both as a protective encapsulation layer and as a support for the light extraction enhancement layer. The encapsulation layer itself is formulated with specific refractive index (1.7-2.0) to participate in light extraction, eliminating the need for separate complex optical management layers and reducing overall device complexity while improving light extraction efficiency
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 light extracting electrode effectively increases the light extraction efficiency of OLED devices by scattering light and reducing the waveguide effect, enhancing the overall light emission from the device.
Implementation Method 1
A light extracting electrode with a metallic layer incorporating light scattering features, such as dendrites or defects, is introduced to disrupt the waveguide effect, increasing the haze and allowing more electromagnetic radiation to be emitted by scattering light randomly
Implementation Method 2
An organic light emitting diode (OLED) is a device having an emissive layer that emits electromagnetic radiation, such as visible light, in response to the application of an electric current
Implementation Method 3
A large portion of the generated electromagnetic energy is trapped within the OLED device due to the 'optical waveguide effect' caused by the reflection of electromagnetic radiation at the interfaces of the various layers of the OLED device
Data Source
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AI summary
An organic light emitting diode (10) includes a substrate (20), a first electrode (12), an emissive active stack (14), and a second electrode (18). At least one of the first and second electrodes (12, 18) is a light extracting electrode (26) having a metallic layer (28). The metallic layer (28) includes light scattering features (29) on and/or in the metallic layer (28). The light extracting features (29) increase light extraction from the organic light emitting diode (10).