m-Terphenyl Derivatives for OLED Electron Transport and Hole Blocking
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Solution Overview
Problem
Current OLED technologies face challenges in achieving a balance between electron and hole transport, leading to inefficiencies and reduced device performance due to the higher triplet energy level of phosphorescent molecules, which causes energy leakage and affects the internal quantum efficiency and lifespan of OLED devices.
Innovation Solution
The development of m-terphenyl derivatives with specific five-membered heterocyclic compounds as electron transport materials, which can function as electron transport, injection, or hole blocking materials, offering improved electron mobility, thermal stability, and exciton blocking properties, thereby enhancing the performance of OLED devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If phosphorescent heavy metals are adopted as phosphorescent dopants in the emitting layer to achieve strong spin-orbital coupling and mixing of singlets and triplets, then the internal quantum efficiency (IQE) is enhanced up to 100%, but the higher triplet energy level causes energy to flow to other materials with lower triplet energy level and cause illumination in the device
Solution Approach 1:
The patent modifies the triplet energy level parameter of the electron transport material by introducing m-terphenyl derivatives with specific heterocyclic structures. This parameter change ensures the electron transport material has a higher triplet energy level than the phosphorescent dopant, preventing energy leakage while maintaining device performance
Solution Approach 2:
The m-terphenyl derivative acts as an intermediary material between the phosphorescent dopant and the host material. It mediates energy transfer by having an appropriate triplet energy level that prevents energy leakage to other materials while still allowing efficient energy transfer from the phosphorescent dopant
2Reliability
If known electron transport materials with hole blocking property are used with HOMO value more than 6 eV, then hole blocking capability is achieved, but electron mobility is insufficient to obtain the combination area departed from the cathode and increase the generation rate of excitons
Solution Approach 1:
The patent optimizes both HOMO and LUMO energy level parameters of the electron transport material. The m-terphenyl derivatives achieve HOMO values greater than 6 eV for hole blocking while simultaneously achieving LUMO values between -2.0 to -3.0 eV for improved electron mobility, resolving the trade-off between these two properties
Solution Approach 2:
The patent uses composite molecular structures combining m-terphenyl core with five-membered heterocyclic compounds (triazole, tetrazole, oxadiazole, thiadiazole). This composite structure integrates both hole blocking capability (from high HOMO) and electron transport capability (from appropriate LUMO and molecular geometry) within a single material
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 use of m-terphenyl derivatives results in improved electron transport and hole blocking capabilities, increasing the internal quantum efficiency, reducing energy leakage, and extending the lifespan of OLED devices by maintaining higher triplet energy levels, thus offering better performance and light purity.
Implementation Method 1
electrons and holes diffuse through an electron transport layer (ETL) and hole transport layer (HTL), respectively, to enter a light-emitting layer
Implementation Method 2
suitable HOMO and LUMO values so as to provide lowered operating voltage for good electron injection and optional hole blocking properties
Implementation Method 3
electrons and holes diffuse through an electron transport layer (ETL) and hole transport layer (HTL), respectively, to enter a light-emitting layer, and recombine in the emitting region to form a particle generally referred as exciton. In order for the exciton to relax to the ground state, the energy is given off in the form of photo radiation
Implementation Method 4
The triplet exciton relaxation would radiate phosphorescence. Phosphorescence achieves 3-fold efficiency when compared to fluorescence and may greatly enhance the IQE (internal quantum efficiency) of devices up to 100% by adopting heavy metal in electroluminescent configuration to achieve strong spin-orbital coupling and mixing of singlets and triplets
Data Source
AI summary
An m-terphenyl derivative has a structure of formula (I) or (II):wherein A and B are five-membered heterocyclic compounds selected from the group consisting of pyrrole, pyrazole, imidazole, 1,2,3-triazole, 1,2,4-triazole, 1,2,3,4-tetrazole, 1,2-thiazole, 1,3-thiazole and 1,3,4-thiadiazole, each of substituents R, R1 and R2 is a member independently selected from the group consisting of H, halo, cyano, trifluoromethyl, amino, C1-C10 alkyl, C2-C10 alkenyl, C2-C10 alkynyl, C3-C20 cycloalkyl, C3-C20 cycloalkenyl, C1-C20 heterocycloalkyl, C1-C20 heterocycloalkenyl, aryl and heteroaryl. The compound of the present invention may have advantages in good electron affinity, low HOMO and thereby achieving hole blocking and may be used for electron transport material and/or electron injection material.