OLED Light Extraction with High Index Substrate
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Solution Overview
Problem
Current organic light emitting diode (OLED) devices face challenges in optimizing light outcoupling efficiency due to limitations in the optical distance between the organic emissive layer and the reflective electrode, leading to significant light loss through internal reflection and surface plasmon modes.
Innovation Solution
The use of a high refractive index substrate (index of 1.5 or greater) and optimizing the optical distance between the organic emissive layer and the reflective electrode, either by increasing the thickness of layers or using a shifting factor to enhance the substrate mode extraction, such as through surface topographic modifications like microlens arrays, to improve light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the optical distance between the organic emissive layer and the reflective electrode is increased to improve light extraction efficiency, then the substrate mode extraction is enhanced, but the device thickness increases
Solution Approach 1:
The patent applies parameter changes by optimizing the optical distance between the organic emissive layer and the reflective electrode to specific values (λ/4, 3λ/4, or 5λ/4 where λ is the emission wavelength). This precise parameter optimization enables constructive interference of light waves, significantly enhancing substrate mode extraction and light extraction efficiency without requiring excessive increases in device thickness
Solution Approach 2:
The patent introduces a high refractive index substrate (with refractive index n ≥ 1.5) as a new dimensional parameter to control light propagation. This substrate parameter creates favorable optical conditions that enhance light extraction efficiency independently of device thickness, effectively adding a new degree of freedom to the optical design
2Ease of manufacture
If conventional substrates with lower refractive index are used, then the device structure is simpler, but significant light loss occurs through internal reflection and surface plasmon modes
Solution Approach 1:
The patent changes the refractive index parameter of the substrate from conventional values (typically < 1.5) to high refractive index values (n ≥ 1.5). This parameter change fundamentally alters the optical properties of the device, reducing internal reflection losses and surface plasmon mode losses while enhancing substrate mode extraction, all while maintaining manufacturing simplicity
Solution Approach 2:
The patent converts what would normally be harmful losses (internal reflection and surface plasmon modes) into beneficial substrate mode extraction. By optimizing the optical distance parameters and using a high refractive index substrate, the patent redirects light that would otherwise be lost into useful substrate modes that can be extracted more efficiently
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 approach significantly enhances the light extraction efficiency by increasing the substrate mode extraction and reducing surface plasmon losses, thereby improving the overall performance of OLED devices without significantly increasing device thickness or material costs.
Implementation Method 1
a high index substrate having an index of refraction of 1.5 or greater
Implementation Method 2
significant light loss through internal reflection and surface plasmon modes
Implementation Method 3
OLEDs make use of thin organic films that emit light when voltage is applied across the device
Implementation Method 4
an optical distance between the organic emissive layer and the reflective electrode of the OLED is between λ/4 and 3λ/4
Implementation Method 5
a reflective electrode
Data Source
AI summary
Embodiments disclosed herein provide an organic light emitting diode (OLED) device is provided, including a high index substrate having an index of refraction of 1.5 or greater, a reflective electrode, an organic emissive layer configured to emit light having a wavelength of λ; and where an optical distance between the organic emissive layer and the reflective electrode of the OLED is between λ/4 and 3λ/4.