Organic EL Element Concentration Gradient Layers
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Solution Overview
Problem
Organic electroluminescence elements face challenges in achieving high light-emission efficiency and durability, particularly due to carrier injectability issues and barriers between layers, which lead to increased driving voltage and reduced durability.
Innovation Solution
An organic electroluminescence element with at least two light-emitting layers, where one layer contains an electron transporting material with increasing concentration towards the cathode and the other layer contains a hole transporting material with decreasing concentration towards the cathode, optimized to enhance carrier transfer and reduce barriers between layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a laminate structure with multiple functional layers is used, then brightness and element efficiency are improved, but carrier injectability is reduced due to barriers between layers
Solution Approach 1:
The patent applies local quality by creating a bipolar mixed layer with a specific concentration gradient of light-emitting materials. This layer has different properties at different positions: the concentration of electron transporting light-emitting material increases from anode side toward cathode side, while hole transporting light-emitting material concentration decreases. This localized variation in composition optimizes carrier injection and transport at each interface region, resolving the contradiction between maintaining high light-emission efficiency and ensuring good carrier injectability across the laminate structure.
Solution Approach 2:
The patent employs parameter changes by systematically varying the concentration of light-emitting materials within the bipolar mixed layer. Specifically, the electron transporting light-emitting material concentration increases from 0% to 50% or more from anode to cathode, while hole transporting light-emitting material concentration decreases correspondingly. This parameter optimization enables the layer to maintain both high carrier injectability and high light-emission efficiency simultaneously.
2Reliability
If concentration gradient of light-emitting material is arranged in restricted region, then carrier transfer resistance is lowered, but light emission occurs only in restricted region reducing overall efficiency
Solution Approach 1:
The patent applies segmentation by dividing the light-emitting layer into distinct functional zones within the bipolar mixed layer. The layer is segmented such that carrier injection and transport occur primarily in specific regions with optimized concentration gradients, while light emission is distributed across the entire layer. This segmentation allows carrier transfer resistance to be lowered in critical interface regions while maintaining broad light emission coverage through the full layer structure.
Solution Approach 2:
The patent uses local quality by creating specific concentration profiles in different regions of the bipolar mixed layer. The electron transporting light-emitting material concentration increases toward the cathode side, while hole transporting light-emitting material concentration decreases, creating locally optimized zones for different carrier types. This enables efficient carrier transfer in restricted regions while maintaining overall high light-emission efficiency across the entire layer.
3Ease of operation
If barrier between layers is reduced to improve carrier injectability, then driving voltage decreases, but durability is reduced
Solution Approach 1:
The patent applies composite materials by creating a bipolar mixed layer that combines both electron transporting and hole transporting light-emitting materials in a specific concentration gradient. This composite structure functions as an intermediate layer that reduces carrier injection barriers and driving voltage while simultaneously providing enhanced durability through the synergistic combination of materials with complementary properties. The composite layer maintains stable electrical characteristics during continuous operation, resolving the contradiction between low driving voltage and high durability.
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 results in high light-emission efficiency and improved durability by ensuring uniform light emission throughout the layers and reducing leakage of charge carriers, maintaining efficiency across a wide current range.
Implementation Method 1
The organic EL element is a device for obtaining luminescence by utilizing luminescence from excitons each of which is obtained by recombining an electron injected from a cathode with a hole injected from an anode to produce the exciton in the light-emitting layer, or luminescence from excitons of other molecules produced by energy transmission from the above-described excitons.
Data Source
AI summary
An organic electroluminescence element including at least two light-emitting layers disposed between an anode and a cathode, wherein the at least two light-emitting layers include a light-emitting layer A that contains an electron transporting light-emitting material and a hole transporting host material, wherein a concentration of the electron transporting light-emitting material gradually increases from an anode side toward a cathode side of the light-emitting layer A, and a light-emitting layer B that contains a hole transporting light-emitting material and an electron transporting host material, wherein a concentration of the hole transporting light-emitting material gradually decreases from an anode side toward a cathode side of the light-emitting layer B. An organic EL element with high light-emission efficiency and excellent durability is provided.