Multilayer Hole Injection Layer for OLED Efficiency and Lifespan
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Solution Overview
Problem
Existing light-emitting devices face challenges in achieving high luminescence efficiency and long lifespan, particularly in terms of driving voltage, current density, and color purity.
Innovation Solution
Incorporating a multi-layered hole injection layer with inorganic materials such as post-transition metals and metalloids, or compounds containing these elements, in the light-emitting device structure, along with specific hole transporting materials and emission layers, to enhance hole injection and transport characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional single-layer hole injection layer is used, then the device structure is simple, but the luminescence efficiency and lifespan are insufficient
Solution Approach 1:
The hole injection layer is divided into multiple sub-layers (first hole injection layer, second hole injection layer, third hole injection layer) with different materials and functions. Each sub-layer targets specific performance aspects: the first layer improves hole injection efficiency, the second layer optimizes charge transport, and the third layer enhances device stability, collectively resolving the lifespan issue while managing structural complexity through functional segmentation.
Solution Approach 2:
The patent employs composite material structures in the hole injection layer, combining organic compounds (e.g., mCP, TCTA, TAPC) with inorganic materials (e.g., MoO3, V2O5, WO3) across different sub-layers. This composite approach leverages the advantages of both material types to achieve superior luminescence efficiency and device lifespan compared to conventional single-material layers.
2Use of energy by moving object
If the driving voltage is reduced to improve energy efficiency, then the current density decreases, but high current density is needed for high luminescence efficiency
Solution Approach 1:
The patent systematically adjusts material parameters (HOMO levels, electron mobility) and structural parameters (layer thicknesses, material compositions) across the three hole injection layers to optimize the voltage-current characteristics. By carefully selecting materials with appropriate energy levels and adjusting layer thicknesses, the device achieves low driving voltage while maintaining high current density through enhanced charge injection and transport efficiency.
3Productivity
If inorganic materials are added to the hole injection layer to improve hole injection, then the luminescence efficiency increases, but the device complexity increases
Solution Approach 1:
Inorganic materials (MoO3, V2O5, WO3) are strategically positioned in specific sub-layers where they provide the most benefit for hole injection and charge transport. The first hole injection layer uses inorganic materials directly adjacent to the anode for optimal hole injection, while subsequent layers use organic materials for charge transport, creating local optimization rather than uniform complexity throughout the entire structure.
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 results in significantly improved luminescence efficiency and extended lifespan of the light-emitting devices with lower driving voltage and higher current density, matching or exceeding the performance of existing technologies.
Implementation Method 1
Holes provided from the first electrode may move toward the emission layer through the hole transport region
Implementation Method 2
Carriers, such as holes and electrons, recombine in the emission layer to produce excitons. These excitons transition from an excited state to a ground state to thereby generate light
Data Source
AI summary
A light-emitting device includes: a first electrode; a second electrode facing the first electrode; and an interlayer between the first electrode and the second electrode and including an emission layer, wherein the interlayer includes a hole injection layer and a hole transport layer between the first electrode and the emission layer, the hole injection layer directly contacts the first electrode, the hole injection layer has a multi-layered structure of at least two different layers that are stacked on each other, the hole injection layer includes at least one inorganic material of a post-transition metal, a metalloid, a compound including at least two post-transition metal elements, a compound including at least two metalloid elements, or a compound including a post-transition metal element and a metalloid element, the post-transition metal and the metalloid are described herein.