Hole Injection Layer for Organic Light Emitting Devices
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Solution Overview
Problem
The existing organic electroluminescent devices face challenges in reducing driving voltage due to difficulties in hole injection between the hole injection layer and the hole transport layer, primarily caused by differences in highest occupied molecular orbital (HOMO) energy levels and interfacial properties.
Innovation Solution
A hole injection layer is formed using a mixture of inorganic materials such as alkali metal oxides, alkaline earth metal oxides, or halogen compounds, combined with organic materials represented by a specific formula, to facilitate easier hole injection and transport, reducing the HOMO energy level difference and improving interfacial properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional hole injection layer materials (DNTPD, IDE406, CuPc) are used, then the device structure is simple, but the driving voltage increases due to poor hole injection caused by HOMO energy level mismatch
Solution Approach 1:
The patent applies composite materials by combining inorganic materials (alkali metal oxides, alkaline earth metal oxides, or halogen compounds) with organic materials (compounds with specific molecular structures containing electron-donating groups) to create a hole injection layer. This composite structure enables effective hole injection from the anode to the hole transport layer by achieving proper energy level alignment, thereby reducing driving voltage while maintaining device functionality.
Solution Approach 2:
The patent changes the energy level parameters of the hole injection layer by selecting inorganic materials with appropriate work functions and organic materials with specific HOMO levels. By adjusting these energy level parameters to match between the anode, hole injection layer, and hole transport layer, the patent optimizes hole injection efficiency and reduces the driving voltage required for device operation.
2Ease of manufacture
If the HOMO energy level difference between hole injection layer and hole transport layer is large, then material selection is easier, but hole injection becomes difficult and driving voltage increases
Solution Approach 1:
The patent systematically adjusts the energy level parameters by selecting inorganic materials with specific work functions (such as LiF, Cs2CO3) and organic materials with tailored HOMO levels (containing electron-donating groups like alkyl, aryl, or heteroaryl substituents). This parameter optimization ensures the HOMO energy level gradient is properly established, enabling efficient hole injection while providing clear material selection criteria.
Solution Approach 2:
The hole injection layer acts as an intermediary between the anode and the hole transport layer, mediating the energy level transition. The inorganic-organic composite structure serves as a buffer that facilitates smooth charge transfer by matching energy levels across the interface, thereby improving hole injection efficiency without requiring extreme material property mismatches.
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 approach effectively decreases the driving voltage required for the organic light emitting device, as demonstrated by reduced driving voltage at a current of 10 mA/cm2, indicating improved hole injection and transport efficiency.
Implementation Method 1
hole injection layer comprises a mixture of an inorganic material comprising at least one of an alkali metal oxide, an alkaline earth metal oxide, a halogen compound of an alkali metal, and a halogen compound of an alkaline earth metal, and an organic substance
Implementation Method 2
reduce a driving voltage due to difficulties in hole injection between the hole injection layer and the hole transport layer, primarily caused by differences in highest occupied molecular orbital (HOMO) energy levels
Implementation Method 3
When charge carriers are injected into an organic film formed between an electron injection electrode (cathode) and a hole injection electrode (anode) of an organic electroluminescent device, electrons combine with holes to create electron-hole pairs, which then decay to emit light
Data Source
AI summary
An organic light emitting device includes an anode, a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, an electron injection layer and a cathode laminated in this order, wherein the hole injection layer comprises a mixture of an inorganic material comprising at the least of one of an alkali metal oxide, an alkaline earth metal oxide, a halogen compound of an alkali metal, a halogen compound of an alkaline earth metal, and an organic material comprising at least one of compounds represented by Formula 1:wherein R1, R2, R3, R4, R5 and R6 are each independently selected from a substituted or unsubstituted C6 to C30 aromatic group and a C5 to C29 heterocyclic group containing N, S, or O, wherein the substituent is selected from a C1 to C6 aliphatic group and a C6 to C12 aromatic group.