Multi-Layered Hole Transport Layer for OLED Efficiency
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Solution Overview
Problem
Conventional light-emitting devices face issues with high driving voltage and short lifespan due to exciton recombination at the interface between the electron blocking layer and the emission layer, leading to deterioration of the device.
Innovation Solution
The introduction of a multi-layered hole transport layer with a doped layer in the light-emitting device, which moves the recombination zone to the interface between two emission layers, improving hole injection characteristics and reducing exciton quenching, and the use of a double-layered emission structure to enhance efficiency and lifespan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional single-layer hole transport layer is used, then the device structure is simple, but the driving voltage is high and the lifespan is short due to exciton recombination at the electron blocking layer interface
Solution Approach 1:
The hole transport layer is divided into multiple functional layers: a first hole transport layer adjacent to the emission layer, a second hole transport layer adjacent to the electron blocking layer, and an optional third hole transport layer between them. This segmentation separates the functions of hole transport and exciton management, preventing exciton recombination at the electron blocking layer interface while maintaining structural organization.
Solution Approach 2:
Different hole transport layers are assigned different materials and properties optimized for their specific locations. The first hole transport layer uses materials with appropriate HOMO levels for efficient hole transport from the emission layer, while the second hole transport layer is positioned to prevent exciton quenching at the electron blocking layer interface, creating locally optimized conditions throughout the structure.
2Device complexity
If the electron blocking layer is removed to simplify the structure, then fewer layers are needed, but exciton recombination control becomes difficult leading to high driving voltage
Solution Approach 1:
The second hole transport layer serves as an intermediary between the emission layer and the electron blocking layer, mediating the interaction between holes and excitons. This intermediate layer prevents direct contact between excitons and the electron blocking layer, eliminating exciton quenching while maintaining the necessary electrical functionality, thereby reducing driving voltage without completely removing the electron blocking layer.
3Reliability
If a multi-layered hole transport structure is introduced, then exciton quenching is reduced and lifespan is extended, but the device structure becomes more complex
Solution Approach 1:
The hole transport layer is divided into multiple functional layers: a first hole transport layer adjacent to the emission layer, a second hole transport layer adjacent to the electron blocking layer, and an optional third hole transport layer between them. This segmentation separates the functions of hole transport and exciton management, preventing exciton recombination at the electron blocking layer interface while maintaining structural organization.
4Use of energy by moving object
If carriers recombine in the emission layer to produce excitons, then light is generated, but exciton recombination at the electron blocking layer interface causes deterioration and short lifespan
Solution Approach 1:
The invention converts the potentially harmful effect of exciton migration toward the electron blocking layer into a beneficial outcome by positioning the second hole transport layer to intercept and recombine holes before they reach the electron blocking layer. This prevents exciton quenching at the interface while maintaining efficient luminescence generation in the emission layer, thus extending device lifespan without sacrificing 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 results in improved driving voltage characteristics, increased efficiency, and a longer lifespan by controlling charge balance and preventing exciton quenching, while maintaining effective blue fluorescence emission without the need for an electron blocking layer.
Implementation Method 1
the doped layer includes a hole transport material and a p-dopant
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.
Implementation Method 3
Holes provided from the first electrode may move toward the emission layer through a non-luminescent exciton transport region
Data Source
AI summary
A light-emitting device includes a first electrode, a second electrode, m emitting units, and m−1 charge generation layers. The m emitting units each include a hole transport region, an emission layer, and an electron transport region. At least one emission layer of the m emitting units includes a first emission layer and a second emission layer, and at least one hole transport region adjacent to a p-type charge generation layer includes a multi-layered hole transport layer consisting of a first non-doped layer, a doped layer, and a second non-doped layer. The first non-doped layer and the second non-doped layer each independently consist of a hole transport material, the doped layer includes a hole transport material and a p-dopant, and the hole transport region adjacent to the first electrode does not include the multi-layered hole transport layer. An electronic apparatus including the light-emitting device is also provided.