Organic Electroluminescence Device Host Material Energy Barrier
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Solution Overview
Problem
Phosphorescent organic electroluminescence devices have shorter lifetimes compared to fluorescent devices due to the diffusion of triplet excitons and require specific material selection and device design to enhance performance.
Innovation Solution
Incorporating a first host material with a partial structure of an aromatic heterocyclic ring containing a nitrogen-containing six-membered ring and a second host material with an aromatic hydrocarbon or heterocyclic ring bonded with a cyano group in the emitting layer to promote efficient recombination of holes and electrons.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a phosphorescent organic EL device uses triplet excitons for emission, then the internal quantum efficiency can be improved up to 100%, but the device lifetime becomes shorter due to diffusion of triplet excitons to neighboring layers
Solution Approach 1:
The patent changes the energy gap parameter of the host material to be larger than that of the phosphorescent dopant material, creating an energy barrier that prevents triplet exciton diffusion to neighboring layers while maintaining efficient energy transfer to the dopant for phosphorescent emission
Solution Approach 2:
The host material acts as an intermediary that confines triplet excitons within the emitting layer through energy gap engineering, preventing their diffusion to electron transporting and hole transporting layers while still enabling efficient energy transfer to the phosphorescent dopant
2Reliability
If a compound with larger energy gap than phosphorescent dopant is used in emitting layer, then triplet exciton diffusion is suppressed, but drive voltage of the overall device increases
Solution Approach 1:
The patent optimizes the energy gap parameter of the host material to achieve the minimum necessary value that is larger than the phosphorescent dopant's energy gap, balancing exciton confinement effectiveness with acceptable drive voltage levels
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 prolongs the lifetime of the organic electroluminescence device by improving carrier balance and luminous efficiency.
Implementation Method 1
When voltage is applied on an organic electroluminescence device, holes and electrons are respectively injected into an emitting layer from an anode and a cathode. The injected electrons and holes are recombined in an emitting layer to form excitons.
Implementation Method 2
In the classification according to the emission principle, in a fluorescent EL device which uses emission caused by singlet excitons
Implementation Method 3
in a phosphorescent EL device which uses emission caused by triplet excitons
Implementation Method 4
since spin is forbidden and a relaxation rate is slow, the triplet excitons are likely to diffuse to the neighboring layers, so that the triplet excitons are thermally energy-deactivated
Data Source
AI summary
An organic electroluminescence device 1 includes: an anode 3, a cathode 4 opposed to the anode 3 and an emitting layer 5 provided between the anode 3 and the cathode 4. The emitting layer 5 contains first and second host materials and a luminescent material. The first host material has a partial structure represented by at least one of the following formulae (1) and (2) while the second host material has a partial structure represented by the following formula (3). Az represents a substituted or unsubstituted aromatic heterocyclic group containing a nitrogen-containing six-membered ring. WCN is an aromatic hydrocarbon group substituted by at least one cyano group (CN) or an aromatic heterocyclic group substituted by at least one cyano group (CN). Ar1 is a substituted or unsubstituted aromatic hydrocarbon group or a substituted or unsubstituted aromatic heterocyclic group, but is not an aromatic heterocyclic group containing a nitrogen-containing six-membered ring.—Az—(WCN)p (1)—Az—(CN)q (2)—Ar1—(CN)r (3)