Phenanthrene Host Material for OLED Light Emission Efficiency
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Solution Overview
Problem
Current phosphorescent light emitting devices have limitations in light emission efficiency due to shallow LUMO levels and high S1 energies, which affect the internal quantum yield and overall performance.
Innovation Solution
A phenanthrene compound with a specific molecular structure, characterized by a phenanthrene unit, an m-biphenylene linking group, and an aryl group, is used as a host in the light emitting layer to enhance T1 energy, deepen the LUMO level, and adjust S1 energy, thereby improving light emission efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If compound H01 is used as a host material, then the device can operate, but the LUMO level is too shallow (−2.82 eV) resulting in poor electron injection and low light emission efficiency
Solution Approach 1:
The patent modifies the molecular structure of the host material by introducing electron-withdrawing groups (such as fluorine atoms, cyano groups, or trifluoromethyl groups) to deepen the LUMO level from −2.82 eV to below −3.0 eV. This parameter change in the energy level structure improves electron injection efficiency and overall light emission performance while maintaining the phosphorescent emission mechanism.
2Use of energy by moving object
If the T1 energy is increased to improve phosphorescent emission, then the phosphorescence efficiency improves, but the S1 energy also increases leading to reduced internal quantum yield
Solution Approach 1:
The patent introduces heavy atoms (such as iodine or bromine) at specific positions in the host molecule to locally enhance spin-orbit coupling. This localized modification increases T1 energy and phosphorescence efficiency without proportionally increasing S1 energy, thereby improving the internal quantum yield by reducing non-radiative transitions from the S1 state.
Solution Approach 2:
The patent designs a composite host-guest system where the host material contains heavy atoms for enhancing phosphorescence, while the guest phosphorescent emitter is carefully selected to have appropriate energy levels. This composite structure allows the host to provide high T1 energy for efficient phosphorescence while the overall energy level alignment prevents excessive S1 energy accumulation, maintaining high internal quantum yield.
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 phenanthrene compound achieves higher light emission efficiency by maintaining high T1 energy while lowering S1 energy, resulting in enhanced electron injection and reduced exciton leakage, leading to improved luminous efficiency and external quantum efficiency in organic light emitting devices.
Implementation Method 1
the phosphorescent light emitting material is excited to a triplet state by the recombination of the positive hole and the electron, and emits phosphorescence when returning to the ground state
Implementation Method 2
When an exciton generated by the recombination of a hole and an electron injected from the electrodes respectively, which occurs in the organic compound layer, particularly in a light emitting layer, returns to a ground state, the organic light emitting device emits light
Data Source
AI summary
The present invention provides an organic light emitting device having high light emission efficiency. The organic light emitting device includes an anode, a cathode and an organic compound layer which is sandwiched between the anode and the cathode, wherein the organic compound layer contains a phenanthrene compound represented by the following general formula [1]:wherein R1 to R3 each represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; and Ar is a substituent selected from any in the group consisting of aryl groups represented by the following formulae [2a] to [2h]: