OLED Electron-Transport Layer Gradient for Longer Device Lifetime
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Solution Overview
Problem
Existing light-emitting devices face challenges in achieving long lifetime, high reliability, low driving voltage, and high emission efficiency.
Innovation Solution
A light-emitting device with a specific layered structure comprising a first electrode, a first light-emitting layer, a first layer containing an electron-transport material and a metal or organometallic salt, a second layer with a lower concentration of the metal or organometallic salt, and a second light-emitting layer, which enhances electron injection and suppresses excess electron injection, thereby improving device characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional organic EL device structure is used, then the device can be formed with ease and provide planar light emission, but the device exhibits short lifetime and low reliability
Solution Approach 1:
The electron-transport region is divided into multiple layers (first electron-transport layer, second electron-transport layer, third electron-transport layer) with progressively decreasing concentrations of electron-transport material. This segmentation allows precise control of electron distribution and injection, resolving the contradiction by achieving high reliability through structured complexity rather than uncontrolled complexity.
Solution Approach 2:
Each electron-transport layer has a distinct local quality characterized by different concentrations of electron-transport material. The first layer has high concentration for strong electron transport, the second layer has medium concentration for transition, and the third layer has low concentration for controlled electron injection suppression. This local differentiation enables the device to achieve both high reliability and controlled complexity.
2Reliability
If electron injection is enhanced to improve emission efficiency, then high emission efficiency is achieved, but excess electron injection occurs causing short device lifetime
Solution Approach 1:
The electron-transport layers create a dynamic gradient structure where electron concentration decreases from the first layer through the second layer to the third layer. This dynamic concentration gradient enables the system to enhance electron injection efficiency in the electron-transport region while automatically suppressing excess electron injection at the interface with the light-emitting layer, thus resolving the contradiction between emission efficiency and device lifetime.
Solution Approach 2:
The invention changes the concentration parameter of electron-transport material across different layers. The first electron-transport layer contains a first concentration, the second layer contains a second concentration lower than the first, and the third layer contains a third concentration lower than the second. This parameter change strategy enables precise control of electron behavior, achieving high emission efficiency while preventing excess electron injection that would shorten device lifetime.
3Use of energy by moving object
If driving voltage is reduced to improve energy efficiency, then energy efficiency improves, but device performance and reliability deteriorate
Solution Approach 1:
The second electron-transport layer acts as an intermediary between the first and third layers, facilitating smooth electron transport from the high-concentration first layer to the low-concentration third layer. This intermediary structure enables efficient electron management that maintains high device performance while allowing operation at lower driving voltages, thus resolving the contradiction between energy efficiency and device performance.
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 device achieves prolonged lifetime, increased reliability, and reduced driving voltage while maintaining high emission efficiency.
Implementation Method 1
The first layer contains a first organic compound and a first substance... The first organic compound is an electron-transport material... which enhances electron injection
Implementation Method 2
The second layer contains a second organic compound... The second organic compound is an electron-transport material... The second layer has a lower concentration of the first substance than the first layer... suppresses excess electron injection
Implementation Method 3
a compound capable of converting a singlet excited state into light emission (also referred to as a fluorescent compound or a fluorescent substance)
Implementation Method 4
a compound capable of converting a triplet excited state into light emission (also referred to as a phosphorescent compound or a phosphorescent substance)
Data Source
AI summary
A light-emitting device with a long lifetime is provided. A light-emitting device with high reliability is provided. The light-emitting device includes a first electrode, a first light-emitting layer, a first layer, a second layer, a third layer, a second light-emitting layer, and a second electrode stacked in this order. The first layer contains a first organic compound and a first substance. The second layer contains a second organic compound. The third layer contains a second substance. The first organic compound is an electron-transport material. The first substance is a metallic salt, a metal oxide, or an organometallic salt. The second organic compound is an electron-transport material. The second substance is an electron-injection material. The second layer has a lower concentration of the first substance than the first layer.