OLED Hole Injection Layer for Balanced Carrier Mobility
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Solution Overview
Problem
The existing organic light-emitting devices (OLEDs) suffer from low current efficiency due to imbalanced hole and electron mobility, which affects their performance.
Innovation Solution
The OLEDs incorporate a hole injection layer with a first hole transport material and a P-type doping material in specific ratios and thicknesses, along with a second hole transport layer of defined composition and thickness, to balance hole and electron concentrations and enhance recombination regions, while also forming a microcavity structure for optimized light extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional OLED structure with simple hole injection layer is used, then device structure is simple, but current efficiency is low due to imbalanced hole and electron mobility
Solution Approach 1:
The hole injection layer is segmented into multiple sub-layers with different functions: a first hole injection sub-layer containing material (I-1) with specific HOMO level (-5.0eV) for effective hole injection from ITO anode, and a second hole injection sub-layer containing material (I-2) with different properties. This segmentation allows each sub-layer to be optimized for its specific function, resolving the contradiction between improving hole injection efficiency and maintaining structural simplicity.
Solution Approach 2:
The patent uses composite material strategies by combining organic hole transport materials with specific inorganic materials (ITO anode) and doping materials. The hole injection layer comprises a composite of materials (I-1) and (I-2) with complementary properties, where (I-1) provides appropriate energy level alignment and (I-2) enhances hole transport. This composite approach improves current efficiency while managing the complexity through systematic material selection.
2Speed
If hole mobility is increased to improve hole transport, then hole transport efficiency improves, but imbalance with electron mobility worsens, reducing current efficiency
Solution Approach 1:
The patent applies local quality by creating spatial variation in hole mobility across different regions of the hole injection layer. The first hole injection sub-layer with material (I-1) has optimized properties for hole injection from the anode, while the second sub-layer with material (I-2) has different properties optimized for hole transport toward the emission layer. This local optimization ensures adequate hole transport speed without creating excessive imbalance with electron mobility, thereby improving current efficiency.
Solution Approach 2:
The patent systematically changes material parameters including HOMO levels, LUMO levels, and carrier mobilities across different layers. Material (I-1) is selected with HOMO level of -5.0eV to match ITO anode work function, while material (I-2) has different electronic properties. The thicknesses of sub-layers are also optimized parameters. These parameter changes allow tuning of hole transport speed to achieve balance with electron mobility, resolving the contradiction between transport efficiency and current 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
This configuration increases current efficiency and reduces driving voltage, leading to improved performance and extended service life of the OLEDs.
Implementation Method 1
materials of the hole injection layer (30) comprise a first hole transport material and a P-type doping material
Implementation Method 2
a first electrode and a hole injection layer which are laminated and form an ohmic contact therebetween
Implementation Method 3
different carriers are combined in the light-emitting material to release their energy in the form of light
Data Source
Figure 1
AI summary
Disclosed is an organic electroluminescent device, comprising a first electrode and a hole injection layer, which are arranged in a superposed manner, wherein the first electrode is in ohmic contact with the hole injection layer, and the carrier mobility rate of the hole injection layer is less than 2 x 10-5CM2V-1S-1. According to the present invention, by means of using a material with a low mobility rate as a hole injection layer, the mobility rate of a hole in the organic electroluminescent device is reduced, so that the concentration of holes in a light-emitting layer of an OLED can be reduced, the number of holes and electrons in the light-emitting layer tend to be balanced, and a composite area of the holes and the electrons are increased, thereby improving the current efficiency of the OLED.