Phenanthrene Host Material for OLED Driving Voltage Reduction
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Solution Overview
Problem
Current light-emitting elements using phosphorescent compounds face challenges with high driving voltage due to host materials like CBP, which have insufficient hole and electron transport capabilities, and high singlet excitation energy, limiting efficiency.
Innovation Solution
A phenanthrene compound with a bipolar property, featuring a phenanthryl group and a dibenzothiophenyl or dibenzofuranyl group bonded through an arylene group, is developed, providing high triplet excitation energy and efficient carrier transport, suitable as a host material for phosphorescent compounds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If CBP is used as host material, then triplet excitation energy is sufficient, but hole and electron transport capabilities are insufficient, leading to high driving voltage
Solution Approach 1:
The patent creates a composite host material system by combining CBP (providing high triplet excitation energy) with a bipolar compound (providing excellent hole and electron transport capabilities). This composite approach allows the host material to simultaneously satisfy both the energy requirement and the charge transport requirement, resolving the contradiction between sufficient triplet excitation energy and low driving voltage.
2Use of energy by moving object
If phosphorescent compound is used, then internal quantum efficiency can reach 75-100%, but concentration quenching and triplet-triplet annihilation occur
Solution Approach 1:
The patent applies local quality by dispersing the phosphorescent compound uniformly throughout the CBP host matrix at optimized concentrations. This spatial distribution strategy ensures that phosphorescent molecules are sufficiently separated to avoid concentration quenching and triplet-triplet annihilation, while still maintaining high internal quantum efficiency through effective energy transfer from the host to the guest molecules.
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 enhances the efficiency of light-emitting elements by reducing driving voltage and increasing luminescence efficiency, enabling effective use in both fluorescent and phosphorescent light-emitting layers.
Implementation Method 1
a phenanthrene compound having a bipolar property and in which a phenanthryl group having an electron-transport property and a dibenzothiophenyl group or a dibenzofuranyl group having a hole-transport property are bonded to each other
Implementation Method 2
by application of voltage to a light-emitting element, electrons and holes are injected into a layer containing the light-emitting organic compound from a pair of electrodes, whereby current flows. Then, these carriers (i.e., electrons and holes) are recombined, whereby the light-emitting organic compound is excited. The light-emitting organic compound returns to the ground state from the excited state, thereby emitting light.
Implementation Method 3
when a compound in which a triplet excited state is converted into luminescence (hereinafter, such a compound is referred to as a 'phosphorescent compound') is used, internal quantum efficiency can be theoretically 75% to 100%
Implementation Method 4
luminescence from the singlet excited state (S*) is referred to as fluorescence
Data Source
AI summary
A novel compound having high triplet excitation energy and a bipolar property is provided. Specifically, a phenanthrene compound represented by General Formula (G1) is provided where R11 to R19 and R21 to R27 separately represent any one of hydrogen, an alkyl group having 1 to 4 carbon atoms, and a substituted or unsubstituted aryl group having 6 to 13 carbon atoms, Ar represents a substituted or unsubstituted arylene group having 6 to 13 carbon atoms, and Z represents a sulfur atom or an oxygen atom. The use of the phenanthrene compound as a host material of a light-emitting layer in the presence of a phosphorescent dopant allows the formation of a light-emitting element with high current efficiency.