OLED Host Material with Low HOMO-LUMO Levels for Efficiency
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Solution Overview
Problem
Current organic light emitting devices face inefficiencies due to the imbalance in charge injection and transport, particularly with the hole transporting layer having a higher conductivity than the electron transporting layer, which affects the overall device efficiency.
Innovation Solution
Incorporating a material with a LUMO energy level of -4 eV or less and a HOMO energy level of -4 eV or less in the hole injecting and/or transporting layer, allowing for improved charge trapping and reduced conductivity, thereby enhancing device efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional low-molecular-weight organic compounds are used as host materials, then the synthesis process is simple, but the photostability is poor and luminance decay occurs rapidly
Solution Approach 1:
The patent uses a composite structure where a low-molecular-weight compound (formula 1) acts as the host material and a phosphorescent dye (formula 2) is doped into it. This composite approach allows the host to provide structural stability and photostability while the dopant provides the desired photoluminescence properties, resolving the contradiction between synthesis simplicity and photostability.
Solution Approach 2:
The patent introduces specific structural features at local positions of the host molecule - namely the carbonyl group at the 2-position and the electron-withdrawing group at the 5-position of the pyridine ring. These localized functional groups with specific electron densities create favorable local environments that enhance overall photostability without complicating the overall synthesis process.
2Device complexity
If conventional host materials are used, then the device structure is simple, but the phosphorescent quantum efficiency is low due to insufficient spin-orbit coupling
Solution Approach 1:
The patent modifies the electronic parameters of the host material by introducing specific functional groups with different electron densities (electron-donating carbonyl group and electron-withdrawing group). This changes the HOMO-LUMO energy gap and spin-orbit coupling parameters, enabling efficient phosphorescent emission while maintaining simple device structure.
Solution Approach 2:
The host material acts as an intermediary that facilitates energy transfer from the phosphorescent dopant to the host, and then to the emitting state. The specific molecular structure of the host enables efficient spin-orbit coupling that mediates the phosphorescent emission process, achieving high quantum efficiency without complex device architecture.
3Reliability
If high-performance host materials with improved photostability are synthesized, then the luminance decay is reduced, but the synthesis process becomes complex and costly
Solution Approach 1:
The patent segments the host material design into a core pyridine ring structure with separately attached functional groups (carbonyl at 2-position, electron-withdrawing group at 5-position). This segmentation allows independent optimization of each component's properties while maintaining overall synthesis feasibility through modular assembly approaches.
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 leads to a significant improvement in the efficiency of the organic light emitting device by optimizing charge injection and transport, as demonstrated by the examples showing higher efficiency and lower drive voltage compared to devices using single-material layers.
Implementation Method 1
a phosphorescent compound which has a phosphorescent maximum wavelength of 420 nm or more in a toluene solution
Data Source
Figure 1
AI summary
The present invention provides an organic light emitting device comprising a first electrode, a second electrode, and at least two organic material layers interposed therebetween, including a light emitting layer, wherein the organic material layers comprise at least one layer of a hole injecting layer, a hole transporting layer and a hole injecting and transporting layer, and at least one of the hole injecting layer, the hole transporting layer and the hole injecting and transporting layer comprises a material with a HOMO energy level of -4 eV or less, and a material with a LUMO energy level of -4 eV or less, and a process for preparing the same.