Multi-Layered Hole Transport Layer for OLED Driving Voltage
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Solution Overview
Problem
Existing organic light-emitting devices face challenges with high driving voltage and reduced efficiency and lifetime due to excessive charge injection and non-radiative quenching at the interface between the hole transport layer and the emission layer, particularly when using single-layered hole transport materials doped with p-type dopants or high-conductivity hole injecting materials.
Innovation Solution
A multi-layered hole transport layer structure is implemented, using hole transport compounds with different energy levels doped with electron acceptors, along with a pyrimidine-based electron transport layer, to facilitate balanced charge injection and transport, reducing non-radiative quenching and enhancing stability and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a single-layered hole transport layer doped with p-type dopants or high-conductivity hole injecting materials is used, then hole injection capability is improved, but driving voltage increases and charge balance deteriorates
Solution Approach 1:
The hole transport layer is divided into multiple sub-layers (first hole transport layer, second hole transport layer, third hole transport layer) with different materials and functions. Each sub-layer has optimized thickness and doping concentration, allowing gradual charge injection and transport while maintaining low driving voltage and good charge balance.
Solution Approach 2:
Different regions of the hole transport layer have different properties: the first hole transport layer near the anode has high hole injection capability with p-type dopants, the second hole transport layer in the middle has optimized transport properties, and the third hole transport layer near the emission layer has controlled doping to prevent excessive charge injection. This local optimization resolves the contradiction between hole injection capability and driving voltage.
2Productivity
If high-conductivity hole injecting materials are used in the hole transport layer, then hole transport efficiency is improved, but non-radiative quenching at the interface with the emission layer increases
Solution Approach 1:
The third hole transport layer adjacent to the emission layer uses a material (compound 301) with optimized properties that provide sufficient hole transport while minimizing non-radiative quenching. The doping concentration in this layer is controlled to prevent excessive charge injection into the emission layer, thus reducing energy loss while maintaining transport efficiency.
Solution Approach 2:
The hole transport layer uses composite material structures with different compounds (compound 35, compound 301, and their doped variants) in different layers. This composite approach allows each layer to contribute its strengths: compound 35 provides good hole injection, while compound 301 provides efficient transport with reduced quenching at the emission layer interface.
3Ease of operation
If p-type dopants are added to the hole transport layer, then hole injection is enhanced, but device lifetime is reduced due to excessive charge injection
Solution Approach 1:
The doping strategy is segmented across different layers: the first hole transport layer uses p-type dopants ( compounds 501, 502) for enhanced hole injection, while the third hole transport layer uses controlled doping to prevent excessive charge injection. This segmentation allows hole injection enhancement where needed while protecting device lifetime by limiting excessive charge injection near the emission layer.
Solution Approach 2:
The doping concentration is optimized as a parameter: 1-3 parts by weight of electron acceptor per 100 parts by weight of hole transport compound in the first and third hole transport layers. This parameter optimization ensures sufficient hole injection capability while preventing excessive charge injection that would reduce 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 multi-layered structure achieves lower driving voltage, improved charge balance, and extended lifetime of the organic light-emitting device, while the pyrimidine-based electron transport layer simplifies manufacturing and enhances luminescent efficiency.
Implementation Method 1
a first hole transport layer disposed between the emission layer and the first electrode, and including a first hole transport compound and a first electron acceptor
Implementation Method 2
an electron transport layer disposed between the emission layer and the second electrode, and including a pyrimidine-based compound
Implementation Method 3
an emission layer disposed between the first electrode and the second electrode
Data Source
AI summary
An organic light-emitting device includes an emission layer between first and second electrodes, a first hole transport layer that is between the emission layer and the first electrode and that includes a first hole transport compound and a first electron acceptor, a second hole transport layer that is between the emission layer and first hole transport layer and that includes a second hole transport compound, a third hole transport layer that is between the emission layer and the second hole transport layer and that includes a third hole transport compound and a second electron acceptor, a fourth hole transport layer that is between the emission layer and the third hole transport layer and that includes a fourth hole transport compound, a buffer layer between the emission layer and the fourth hole transport layer, and an electron transport layer that includes a pyrimidine-based compound.