OLED Two Hole Transport Layers for Efficiency and Life
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Solution Overview
Problem
Conventional single host OLEDs suffer from low current efficiency and short service life, while dual host OLEDs require high process stability and are sensitive to host material ratio variations, affecting product yield.
Innovation Solution
An organic light-emitting display with two hole transport layers, where the second hole transport layer acts as both an electron blocking and optical compensation layer, combined with a thermal activation delay fluorescent material in the organic light-emitting layer, to enhance current efficiency and service life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single host OLED structure is used, then the device structure is simple, but the current efficiency is low and service life is short
Solution Approach 1:
The hole transport function is segmented into two separate layers: the first hole transport layer (HTL1) and the second hole transport layer (HTL2). HTL1 is responsible for hole injection and initial transport, while HTL2 serves as an electron blocking layer and optical compensation layer. This segmentation allows each layer to be optimized for its specific function, improving overall device performance without significantly increasing structural complexity.
Solution Approach 2:
The second hole transport layer (HTL2) is designed to perform multiple functions simultaneously: it acts as a hole transport layer, an electron blocking layer, and an optical compensation layer. This multi-functionality reduces the need for additional separate layers, maintaining structural simplicity while improving current efficiency and service life through enhanced carrier balance and reduced exciton quenching.
2Reliability
If a dual host OLED structure is used, then carrier balance is improved, but process stability requirement increases and product yield decreases
Solution Approach 1:
Different regions of the hole transport function are assigned to different layers with locally optimized properties. The first hole transport layer uses materials optimized for hole injection and transport, while the second hole transport layer uses materials specifically selected for electron blocking and optical compensation. This local optimization allows each layer to perform its specific function effectively without requiring precise control of dual host material ratios throughout the entire structure.
Solution Approach 2:
The patent employs conventional, well-established organic materials for the hole transport layers that are easier to manufacture and more stable during processing compared to the dual host emitting layer. This approach uses readily available, process-stable materials for the transport functions while reserving the more sensitive dual host structure only for the light-emitting function, thereby improving overall manufacturability and product yield.
3Device complexity
If conventional hole transport layers are used, then the device structure is simple, but current efficiency and service life are insufficient
Solution Approach 1:
The hole transport function is divided into two distinct layers with different material compositions and thicknesses. The first hole transport layer (5-20 nm) focuses on hole injection and initial transport, while the second hole transport layer (20-50 nm) provides electron blocking and optical compensation. This segmentation enables each layer to be optimized for its specific function, significantly improving current efficiency and service life.
Solution Approach 2:
The patent optimizes specific parameters of the hole transport layers, including material selection based on HOMO/LUMO energy levels, layer thicknesses (5-20 nm for HTL1, 20-50 nm for HTL2), and triplet state energy levels (>2.5 eV for HTL2). These parameter optimizations enhance carrier balance, reduce exciton quenching, and improve overall device performance without excessive structural complexity.
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 significantly improves current efficiency and service life of the OLED while maintaining process stability, with the second hole transport layer's dual functionality and thermal activation delay fluorescent material effectively addressing the limitations of single host OLEDs.
Implementation Method 1
the light-emitting material includes a thermal activation delay fluorescent material
Data Source
Figure 1
Figure 2
AI summary
An organic light-emitting display device (100). A functional structure layer (130) of the organic light-emitting display device (100) comprises a hole injection layer (131), a first hole transport layer (1321), a second hole transport layer (1322), an organic light-emitting layer (133), an electron transport layer (134) and an electron injection layer (135) which are sequentially laminated on a first electrode (110). The highest occupied orbital energy level of the material of the first hole transport layer (1321) is less than the highest occupied orbital energy level of the second hole transport layer (1322). A triplet state energy level of the material of the second hole transport layer (1322) is greater than 2.5 eV. The organic light-emitting layer (133) comprises a main light-emitting material, and the main light-emitting material comprises a thermal activation delay fluorescent material. The organic light-emitting display device (100) adopts two hole transport layers, wherein the second hole transport layer (1322) acts as both an electron blocking layer and an optical compensation layer, and matches the thermal activation delay fluorescent material in the organic light-emitting layer (133), thereby improving the current efficiency and service life of the organic light-emitting display device (100).