Organic Electroluminescence Element Host Material Design
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Solution Overview
Problem
Organic electroluminescence devices using carbazole hosts for blue emission suffer from shortened device lifetime and inefficient luminous efficiency, particularly when multiple hosts are combined in green-red emitting layers.
Innovation Solution
An organic electroluminescence device with an emitting layer containing a first host and a second host, both with triplet energies of 2.8 eV or more, and an ionization potential of 5.5 eV or less, where the affinity of the first host is smaller than that of the second host, and the phosphorescent dopant has an emission peak of 480 nm or less, enhancing carrier balance and recombination efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a carbazole host with large triplet energy is used for blue emission, then blue emission is enabled, but the device lifetime is shortened
Solution Approach 1:
The patent uses a composite host system comprising two different hosts (first host and second host) in the emitting layer. The first host has triplet energy of 2.8 eV or more and ionization potential of 5.5 eV or less, while the second host has higher electron affinity. This composite structure enables blue emission through the first host while the second host improves carrier balance and reduces degradation, thereby extending device lifetime.
Solution Approach 2:
The patent assigns different functional roles to different hosts within the emitting layer. The first host is optimized for blue emission with appropriate triplet energy, while the second host is optimized for electron transport and carrier balance. This local differentiation of material properties allows each component to perform its specific function optimally without compromising the other.
2Use of energy by moving object
If multiple emitting layers are layered to improve luminous efficiency, then efficiency is improved, but the device lifetime is shortened due to combined use of carbazole hosts
Solution Approach 1:
The patent applies different host materials to different emitting layers based on their specific requirements. The first host (with high triplet energy and low ionization potential) is used in the blue-emitting layer, while the second host (with higher electron affinity) is used in green-red emitting layers. This localized optimization allows each layer to achieve high efficiency while the second host provides protective effects that extend overall device lifetime.
Solution Approach 2:
The patent employs a composite host system where the first and second hosts work synergistically across multiple emitting layers. The second host, with its higher electron affinity, helps balance carrier distribution and reduce degradation in all emitting layers, thereby extending device lifetime while maintaining the high luminous efficiency achieved through the multi-layer structure.
3Illumination intensity
If a carbazole host with large triplet energy is used, then blue emission is achieved, but carrier balance deteriorates
Solution Approach 1:
The patent optimizes carrier balance by assigning different hosts with complementary properties to different functions. The first host provides the necessary triplet energy for blue emission, while the second host, with its higher electron affinity, specifically addresses electron transport and carrier balance. This functional differentiation resolves the contradiction between achieving blue emission and maintaining carrier balance.
Solution Approach 2:
The second host acts as an intermediary that mediates between the blue-emitting first host and the charge transport layers. It facilitates better electron transport and carrier balance without compromising the blue emission capability of the first host, thereby resolving the carrier balance deterioration issue.
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 solution results in a long-life organic electroluminescence device capable of blue emission with high efficiency, reducing the deterioration of hole and electron transporting layers and extending the device's operational lifespan.
Implementation Method 1
an organic phosphorescent material is used in an emitting layer... uses excited states of the organic phosphorescent material, i.e., a singlet state and a triplet state
Implementation Method 2
when an electrical field is applied, a fluorescent material emits light using energy generated by a recombination of holes injected from an anode with electrons injected from a cathode
Data Source
AI summary
An organic electroluminescence device (1) includes: an anode (3); a cathode (4); and an emitting layer (5) provided between the anode (3) and the cathode (4). The emitting layer contains a first host, a second host and a phosphorescent dopant. A triplet energy of each of the first host and the second host is 2.8 eV or more. An ionization potential of the first host is 5.5 eV or less. An affinity Af1 of the first host is smaller than an affinity Af2 of the second host.