Light-emitting device, display device, light-emitting apparatus, electronic device, and lighting device
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Low outcoupling efficiency is a challenge in organic light-emitting devices (OLEDs), which hinders their performance and efficiency.
Innovation Solution
A cap layer with a high refractive index, ranging from 1.90 to 2.40, and a low extinction coefficient, ranging from 0 to 0.01, is introduced in OLEDs. This cap layer is designed to enhance the outcoupling efficiency of light emitted by the device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a low refractive index material is used in the EL layer to improve outcoupling efficiency, then light extraction is enhanced, but the overall emission efficiency remains insufficient due to limited refractive index contrast
Solution Approach 1:
The device is segmented into multiple functional layers with distinct refractive index characteristics: a cap layer with high refractive index (1.7-2.2) for light extraction enhancement, an EL layer with low refractive index (1.3-1.6) for reduced internal reflection, and a substrate layer. This segmentation allows each layer to be optimized independently for its specific function, achieving superior outcoupling efficiency while maintaining manufacturing feasibility through standardized layer-by-layer fabrication processes.
Solution Approach 2:
The patent applies parameter changes by selecting materials with specific refractive index values within defined ranges. The cap layer uses materials with refractive index 1.7-2.2 (e.g., TiO2, Nb2O5, Ta2O5), while the EL layer uses materials with refractive index 1.3-1.6. These precise parameter selections maximize the refractive index contrast at interfaces, thereby enhancing light outcoupling efficiency without requiring complex device architectures.
2Productivity
If multiple layers with different refractive indices are introduced to enhance light outcoupling, then emission efficiency improves, but manufacturing complexity increases
Solution Approach 1:
The patent simplifies manufacturing by defining specific refractive index ranges for each layer rather than requiring precise thickness control or complex material compositions. The cap layer (refractive index 1.7-2.2) and EL layer (refractive index 1.3-1.6) can be fabricated using standard deposition techniques with routine process control, making the multi-layer structure manufacturable while achieving high emission efficiency through optimized optical parameters.
3Loss of energy
If the refractive index of the cap layer is increased to improve light extraction, then outcoupling efficiency enhances, but absorption losses may increase if the extinction coefficient is not controlled
Solution Approach 1:
The patent simultaneously optimizes two critical optical parameters of the cap layer material: refractive index (1.7-2.2) for enhanced light extraction and extinction coefficient (≤0.05 in the visible range) to minimize absorption losses. This dual parameter optimization ensures that high refractive index materials like TiO2, Nb2O5, and Ta2O5 provide maximum outcoupling efficiency without significant parasitic absorption, resolving the trade-off between light extraction and absorption losses.
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 implementation of the high refractive index cap layer significantly improves the emission efficiency of OLEDs, leading to enhanced light output and reduced power consumption.
Implementation Method 1
a cap layer which includes a high refractive index material having an ordinary refractive index of higher than or equal to 1.90 and lower than or equal to 2.40
Implementation Method 2
an ordinary extinction coefficient of higher than or equal to 0 and lower than or equal to 0.01
Implementation Method 3
an organic compound layer containing a light-emitting material (an EL layer) Carriers are injected by application of a voltage to the device, and recombination energy of the carriers is used, whereby light emission can be obtained
Data Source
AI summary
A light-emitting device with high emission efficiency is provided. The light-emitting device includes an EL layer and a light-transmitting electrode. The EL layer includes a light-emitting layer and a low refractive index layer. The low refractive index layer is positioned between the light-emitting layer and the light-transmitting electrode. A cap layer is in contact with a surface of the light-transmitting electrode on the side opposite to the EL layer. The cap layer includes a high refractive index material having an ordinary refractive index of higher than or equal to 1.90 and lower than or equal to 2.40 and an ordinary extinction coefficient of higher than or equal to 0 and lower than or equal to 0.01. The low refractive index layer includes a low refractive index material having an ordinary refractive index of higher than or equal to 1.60 and lower than or equal to 1.70.