LED Hole Transport Layer Structure for Higher Light Extraction
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Solution Overview
Problem
Current light emitting diodes (LEDs) in display devices face challenges in achieving high emission efficiency and longevity, as existing materials and structures do not effectively optimize light extraction and emission efficiency.
Innovation Solution
A light emitting diode structure is developed with multiple hole transport layers having different refractive indices, specifically a first, second, and third hole transport layer with refractive index differences, to enhance light emission efficiency by minimizing extinction and inducing constructive interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional single-layer hole transport structure is used, then the device structure is simple, but the light extraction efficiency is insufficient
Solution Approach 1:
The hole transport region is divided into multiple hole transport layers (first, second, and third hole transport layers) with different refractive indices. This segmentation allows each layer to contribute differently to light extraction, with the high refractive index third layer positioned adjacent to the emission layer to maximize light extraction efficiency while maintaining reasonable structural complexity.
Solution Approach 2:
Different hole transport layers are assigned different refractive indices tailored to their specific positions and functions. The third hole transport layer adjacent to the emission layer has a higher refractive index (1.7-2.0) to optimize local light extraction at the emission interface, while other layers have lower refractive indices (1.3-1.6) to maintain overall structural efficiency.
2Loss of energy
If multiple hole transport layers with different refractive indices are used, then light extraction efficiency is improved, but the device structure becomes more complex
Solution Approach 1:
The hole transport region is segmented into three distinct layers with progressively different refractive indices, allowing optimized light extraction without requiring excessive structural complexity. The segmentation is functional rather than arbitrary, with each layer serving a specific optical and electrical transport purpose.
Solution Approach 2:
The refractive index parameter is systematically varied across the hole transport layers to optimize light extraction efficiency. By changing this optical parameter rather than structural geometry, the patent achieves improved light extraction without proportionally increasing structural complexity.
3Ease of manufacture
If existing materials are used in the emission layer, then material selection is straightforward, but emission efficiency and device longevity are insufficient
Solution Approach 1:
The emission layer is constructed using composite materials including quantum dots (such as CdSe, CdTe, InP, or perovskite quantum dots) combined with organic or inorganic matrix materials. This composite approach enables tunable emission wavelengths and improved stability, achieving both high emission efficiency and extended device longevity while maintaining reasonable material selection flexibility.
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 use of multiple hole transport layers with varying refractive indices improves light extraction and emission efficiency, leading to higher luminance and extended device life in display devices.
Implementation Method 1
a third hole transport layer disposed between the first hole transport layer and the second hole transport layer, the third hole transport layer having a third refractive index which is greater than each of the first refractive index and the second refractive index
Implementation Method 2
to enhance light emission efficiency by minimizing extinction and inducing constructive interference
Data Source
AI summary
A light emitting diode of an embodiment includes a first electrode, a hole transport region disposed on the first electrode, an emission layer disposed on the hole transport region, an electron transport region disposed on the emission layer, and a second electrode disposed on the electron transport region. The hole transport region includes a first hole transport layer disposed adjacent to the first electrode and having a first refractive index, a second hole transport layer disposed adjacent to the emission layer and having a second refractive index, and a third hole transport layer disposed between the first hole transport layer and the second hole transport layer and having a third refractive index which is greater than each of the first refractive index and the second refractive index, thereby showing high light extraction efficiency and high emission efficiency properties.