Organic EL Device Light-Emitting Layer Concentration Gradient
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Solution Overview
Problem
Organic electroluminescent devices face challenges in achieving high light emission efficiency and durability, with existing solutions either reducing brightness, increasing driving voltage, or limiting light emission to specific regions within the device.
Innovation Solution
An organic electroluminescent device with a light-emitting layer containing a hole transporting host material and an electron transporting phosphorescent material, where the concentration of the phosphorescent material decreases from the cathode to the anode side, enabling uniform light emission across the layer and improving durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If an interfacial layer is provided as a barrier layer between the light-emitting layer and the hole-transport layer to delay hole movement and adjust carrier balance, then external quantum efficiency is raised, but brightness is reduced and driving voltage increases
Solution Approach 1:
The patent applies local quality by creating an interfacial layer with specific properties (containing hole-transport material and electron-transport material in a weight ratio of 95:5 to 50:50) at the boundary between the light-emitting layer and hole-transport layer. This localized structural modification optimizes carrier transport at the critical interface region, improving external quantum efficiency without requiring a complete barrier layer that would block all carrier movement and reduce brightness.
2Loss of energy
If an interfacial layer is provided as a barrier layer to delay hole movement, then external quantum efficiency is raised, but driving durability is reduced
Solution Approach 1:
The patent applies parameter changes by precisely controlling the weight ratio of hole-transport material to electron-transport material in the interfacial layer (95:5 to 50:50). This parameter optimization allows the interfacial layer to delay hole movement sufficiently to improve external quantum efficiency while maintaining adequate carrier transport to preserve driving durability, avoiding the extreme case of a complete barrier layer.
3Stability of the object's composition
If light-emitting units are separated by an insulating layer with opposing electrodes, then individual light emission is achieved, but light extraction is inhibited and external quantum efficiency is poor
Solution Approach 1:
The patent applies the taking out principle by removing the insulating layer that was separating light-emitting units. Instead, the invention uses an interfacial layer with specific material composition (hole-transport material and electron-transport material in controlled ratios) to achieve the necessary functional separation while maintaining optical transparency, thereby extracting the harmful insulating barrier while preserving the beneficial unit separation.
4Loss of energy
If light emission is concentrated at the cathode region to address polymer dispersed type device problems, then injection and transport balance is improved, but the entire light-emitting layer is not utilized effectively
Solution Approach 1:
The patent applies local quality by creating an interfacial layer with optimized material composition at the boundary region between the light-emitting layer and hole-transport layer. This localized modification improves carrier balance and recombination efficiency at the critical interface without preventing light emission from occurring throughout the entire light-emitting layer, thus maintaining high total light emission 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 solution enhances light emission efficiency and durability by allowing light emission from the entire light-emitting layer, reducing efficiency losses at high current regions, and maintaining high performance across a wide current range.
Implementation Method 1
an electron transporting phosphorescent material, where the concentration of the phosphorescent material decreases from the cathode to the anode side
Implementation Method 2
a hole transporting host material
Implementation Method 3
light emission from excitons generated by recombination of electrons injected from a cathode and holes injected from an anode in a light-emitting layer
Implementation Method 4
light emission from excitons of other molecules generated by energy transfer from at least one of the excitons
Data Source
AI summary
An organic EL device includes at least a light-emitting layer provided between a pair of electrodes. The light-emitting layer includes at least a hole transporting host material and an electron transporting phosphorescent material, and the concentration of the electron transporting phosphorescent material in the light-emitting layer decreases from a cathode side toward an anode side.