Red OLED Light-Emitting Element with Dual Electron Transport Layers
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Solution Overview
Problem
The existing image-forming apparatuses using electrophotographic methods face challenges in increasing image resolution due to limitations in arranging inorganic LEDs, and organic electroluminescent elements, despite their potential, have insufficient lifetime for exposure heads.
Innovation Solution
A light-emitting element with a structure comprising a cathode, an anode, a luminescent layer, a first electron transport layer, and a second electron transport layer, where the luminescent layer contains red luminescent materials like diindenoperylene derivatives, and the second electron transport layer includes tris(8-quinolinolate)aluminum and rubrene derivatives, preventing hole transfer and enhancing lifetime.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If organic electroluminescent elements are used as light-emitting elements in exposure heads, then more elements can be arranged in a unit area to increase resolution, but the lifetime of the light-emitting elements becomes insufficient
Solution Approach 1:
The patent changes the chemical composition parameters of the electron transport layers by selecting specific materials (Alq3 for the second layer and Bphen for the first layer) with optimized molecular structures and electron mobility characteristics. This material parameter optimization enables the luminescent layer to achieve both high luminance output and extended operational lifetime, resolving the contradiction between performance and durability
Solution Approach 2:
The patent employs a composite structure with two distinct electron transport layers, each made of different materials optimized for specific functions. The Alq3-based second layer provides hole capture capability while the Bphen-based first layer ensures efficient electron transport. This composite material approach enables the system to simultaneously achieve high luminance, long lifetime, and resistance to hole-induced deterioration
2Illumination intensity
If high current is applied between cathode and anode to increase luminance, then the luminescent layer emits brighter red light, but holes transfer closer to the cathode causing deterioration and reduced lifetime
Solution Approach 1:
The patent introduces the second electron transport layer containing Alq3 as an intermediary barrier between the luminescent layer and the cathode. This intermediate layer acts as a hole trap that captures holes before they can reach the cathode interface, preventing deterioration. The Alq3 material specifically provides hole capture capability while maintaining electron transport function, thus protecting the system from high-current damage while preserving high luminance output
Solution Approach 2:
The patent converts the potentially harmful effect of hole accumulation near the cathode into a beneficial mechanism by designing the Alq3-based second electron transport layer to actively capture and trap these holes. Instead of allowing holes to cause deterioration at the cathode interface, the system redirects them into the second layer where they are harmlessly trapped, transforming a reliability problem into a protective mechanism that extends device lifetime
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 proposed solution results in a long-life, high-luminance red light-emitting element that enhances the reliability and resolution of exposure heads and image-forming apparatuses by extending the lifetime and reducing driving voltage.
Implementation Method 1
In this type of light-emitting element, electrons and holes are injected to the luminescent layer respectively from the cathode and the anode by applying an electric field between the cathode and the anode, and the electrons and the holes are recombined to each other to form excitons in the luminescent layer. When the excitons return to the ground state, the energy is emitted as light.
Implementation Method 2
Tris(8-quinolinolate)aluminum (Alq3) can capture holes. Accordingly, the second electron transport layer containing Alq3 can capture holes having passed through the luminescent layer from the anode toward the cathode.
Data Source
AI summary
A light-emitting element includes a cathode, an anode, a luminescent layer disposed between the cathode and the anode, a first electron transport layer disposed between the luminescent layer and the cathode, and a second electron transport layer in contact with the luminescent layer and the first electron transport layer between the luminescent layer and the first electron transport layer. The luminescent layer contains a red luminescent material emitting red light. The first electron transport layer contains a first electron transport material. The second electron transport layer contains a second electron transport material different from the first electron transport material.