Exciplex-Forming Light-Emitting Element for High External Quantum Efficiency
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Solution Overview
Problem
Existing organic electroluminescence (EL) elements have limited external quantum efficiency, typically ranging from 20% to 30%, due to factors such as light absorption by electrodes and concentration quenching in phosphorescent compounds.
Innovation Solution
A light-emitting element is designed with a light-emitting layer containing a phosphorescent compound, a first organic compound, and a second organic compound, where the combination of these compounds forms an exciplex. This exciplex facilitates energy transfer to the phosphorescent compound, enhancing emission efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a phosphorescent compound is used in the light-emitting layer, then internal quantum efficiency can theoretically reach 100%, but external quantum efficiency is limited to approximately 25% due to light absorption by electrodes and concentration quenching
Solution Approach 1:
The patent introduces an exciplex-forming host material as an intermediary between the phosphorescent compound and the electrodes. This host material forms an exciplex that emits light with a longer wavelength, which reduces absorption by the electrodes and improves external quantum efficiency while maintaining high internal quantum efficiency through effective energy transfer to the phosphorescent compound.
Solution Approach 2:
The patent changes the emission wavelength parameter by using a host material whose exciplex emission overlaps with the absorption band of the phosphorescent compound. This parameter change enables efficient energy transfer while simultaneously reducing electrode absorption losses, resolving the contradiction between internal and external quantum efficiency.
2Reliability
If the phosphorescent compound is dispersed in a host material matrix to suppress concentration quenching, then emission efficiency improves, but light extraction efficiency remains limited at 20-30%
Solution Approach 1:
The host material serves as a dual-function intermediary: it disperses the phosphorescent compound to prevent concentration quenching while simultaneously forming an exciplex that emits at a longer wavelength, reducing electrode absorption and improving light extraction efficiency beyond the conventional 20-30% limit.
3Illumination intensity
If the light-emitting layer is formed with high phosphorescent compound concentration to maximize light emission, then emission intensity increases, but concentration quenching occurs reducing efficiency
Solution Approach 1:
The host material acts as a mediator that accepts energy from the phosphorescent compound and re-emits it through exciplex formation. This allows the use of lower phosphorescent compound concentrations, preventing concentration quenching while maintaining high emission intensity through the exciplex emission pathway.
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 an exciplex in the light-emitting element significantly improves external quantum efficiency, potentially exceeding 30%, while also extending the lifetime of the element by reducing deactivation of excitation energy.
Implementation Method 1
a combination of the first organic compound and the second organic compound forms an exciplex. The exciplex acts on the phosphorescent compound so that the phosphorescent compound emits phosphorescence
Implementation Method 2
light emission from the triplet excited state (T*) is referred to as phosphorescence where electron transition occurs between different spin multiplicities
Data Source
AI summary
A light-emitting element having high external quantum efficiency is provided. A light-emitting element having a long lifetime is provided. Alight-emitting element is provided which includes a light-emitting layer containing a phosphorescent compound, a first organic compound, and a second organic compound between a pair of electrodes, in which a combination of the first organic compound and the second organic compound forms an exciplex (excited complex). The light-emitting element transfers energy by utilizing an overlap between the emission spectrum of the exciplex and the absorption spectrum of the phosphorescent compound and thus has high energy transfer efficiency. Therefore, a light-emitting element having high external quantum efficiency can be obtained.