OLED Light Extraction via Optical Isolation Cavity
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Solution Overview
Problem
Existing OLED devices suffer from significant light loss due to internal reflection, with up to 80% of generated photons being trapped, leading to inefficiencies in light output and reduced sharpness in pixellated applications.
Innovation Solution
A bottom-emitting OLED device structure incorporating an optical isolation cavity with a refractive index lower than the substrate, a transparent electrode, and a light-scattering layer, where the transparent electrode or a second layer has openings leading to the cavity, formed by etching a sacrificial layer, to reduce internal reflection and enhance light extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a typical bottom-emitting OLED device structure is used with standard refractive index materials, then the device structure is simple and easy to manufacture, but up to 80% of generated light is trapped by internal reflection and lost
Solution Approach 1:
The patent introduces an optical isolation cavity with a sacrificial layer as an intermediary structure between the substrate and the OLED layers. This cavity, when filled with a material of lower refractive index than the substrate, acts as an optical mediator that reduces internal reflection at the substrate-OLED interface, thereby improving light extraction efficiency without fundamentally redesigning the entire device structure
Solution Approach 2:
The patent changes the refractive index parameter by introducing an optical isolation cavity that can be filled with materials having different refractive indices than the substrate. By controlling the refractive index of the cavity filling material to be lower than the substrate, the patent optimizes optical coupling and reduces total internal reflection, thereby improving light extraction efficiency
2Loss of energy
If light is emitted in all directions from the internal layers, then complete light coverage is achieved, but most light is trapped and absorbed by the substrate and organic layers
Solution Approach 1:
The optical isolation cavity serves as an intermediary optical path that allows light to escape from the OLED device before it can be trapped and absorbed by the substrate or organic layers. The cavity provides an alternative extraction path that reduces the probability of light being absorbed, thereby reducing energy loss
3Loss of energy
If the encapsulating cover is coated directly over the second electrode with no gap, then the device structure is compact and rigid, but light extraction efficiency is reduced
Solution Approach 1:
The optical isolation cavity acts as an intermediary optical structure that improves light extraction without requiring changes to the encapsulation structure. By providing a refractive index mismatch at the substrate interface, the cavity enables better light extraction while maintaining the standard encapsulation approach
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 increases light output and improves the sharpness of OLED devices by effectively redirecting trapped light, reducing absorption losses, and minimizing the impact of internal reflections, thereby enhancing the overall efficiency and performance of OLED devices.
Implementation Method 1
Due to the high optical indices of the organic materials used, most of the photons generated by the recombination process are actually trapped in the devices due to total internal reflection
Implementation Method 2
a light-scattering layer formed over the optical isolation cavity
Data Source
AI summary
A bottom-emitting organic light-emitting diode (OLED) device, comprising: a transparent substrate; an optical isolation cavity formed over the substrate having a refractive index lower than the refractive index of the substrate; a transparent electrode formed over the optical isolation cavity; one or more layers of organic light-emitting material formed over the transparent electrode; a second electrode formed over the one or more layers of organic light-emitting material; and a light-scattering layer formed over the optical isolation cavity; wherein the transparent electrode or a second layer formed between the optical isolation cavity and the transparent electrode comprises one or more openings leading to the optical isolation cavity, and the cavity is formed by etching a sacrificial layer deposited between the substrate and the transparent electrode or the second layer through the one or more openings.