Exciplex Light-Emitting Layer for Efficient Phosphorescent EL
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing organic electroluminescent (EL) elements face limitations in external quantum efficiency (approximately 25%) and drive voltage, with conventional designs failing to achieve theoretical internal quantum efficiency of 100% due to inefficient energy transfer from host to guest materials, particularly from the singlet excited state.
Innovation Solution
Incorporating a light-emitting layer with a phosphorescent compound and a combination of first and second organic compounds that form an exciplex, where the exciplex's emission spectrum overlaps with the phosphorescent compound's absorption band on the longest wavelength side, facilitating efficient energy transfer from both singlet and triplet excited states.
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 reach 100%, but external quantum efficiency is limited to approximately 25% due to light extraction efficiency of 20-30%
Solution Approach 1:
The patent introduces an exciplex system as an intermediary between the phosphorescent compound and the host material. The exciplex emission spectrum is designed to overlap with the phosphorescent compound's absorption band, creating an efficient energy transfer pathway that overcomes the light extraction efficiency limitation and enables external quantum efficiency to exceed the conventional 25% ceiling.
Solution Approach 2:
The patent optimizes specific parameters of the exciplex system, including the emission spectrum peak wavelength and its overlap integral with the phosphorescent compound's absorption band. By adjusting these parameters to maximize spectral overlap, the energy transfer efficiency is enhanced, allowing external quantum efficiency to surpass the traditional limit imposed by light extraction efficiency.
2Reliability
If conventional host material is used to disperse the phosphorescent compound, then concentration quenching is suppressed, but energy transfer from the singlet excited state of the host to the phosphorescent compound is inefficient
Solution Approach 1:
The patent creates a composite light-emitting layer containing the phosphorescent compound, host material, and exciplex-forming compounds. This composite structure enables dual energy transfer pathways: one from the host's triplet state and another from the exciplex's singlet excited state, both efficiently transferring energy to the phosphorescent compound while maintaining dispersion that prevents concentration quenching.
Solution Approach 2:
The exciplex acts as an intermediary energy transfer mediator between the host material and the phosphorescent compound. The exciplex's emission spectrum is specifically designed to overlap with the phosphorescent compound's absorption band, creating a resonant energy transfer pathway that significantly improves transfer efficiency compared to conventional host-guest systems.
3Reliability
If the phosphorescent compound is dispersed in a host material matrix, then concentration quenching is suppressed, but drive voltage remains high due to inefficient energy transfer
Solution Approach 1:
The exciplex system serves as an intermediary that bridges the energy gap between the host material and phosphorescent compound. By designing the exciplex emission spectrum to overlap with the phosphorescent compound's absorption band, the patent creates an efficient energy transfer pathway that reduces energy loss and lowers the drive voltage required to achieve effective light emission.
Solution Approach 2:
The patent optimizes the energy level parameters of the exciplex system, specifically adjusting the emission spectrum peak wavelength to match the phosphorescent compound's absorption characteristics. This parameter optimization minimizes energy loss during transfer, thereby reducing the electrical voltage needed to drive the light-emitting element while maintaining effective phosphorescent emission.
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 achieves external quantum efficiency exceeding 27%, surpassing conventional limits, and reduces drive voltage by enabling efficient energy transfer and minimizing deactivation processes, resulting in a high-emission efficiency light-emitting element.
Implementation Method 1
an emission spectrum of the exciplex overlaps with an absorption band located on the longest wavelength side of an absorption spectrum of the phosphorescent compound
Implementation Method 2
light emission from the triplet excited state (T*) is referred to as phosphorescence where electron transition occurs between different spin multiplicities
Implementation Method 3
by application of voltage with a light-emitting layer interposed between electrodes, electrons and holes injected from the electrodes are recombined to make a light-emitting substance excited, and light is emitted when the excited state relaxes to the ground state
Data Source
AI summary
Provided is a light-emitting element which includes a light-emitting layer containing a phosphorescent compound, a first organic compound, and a second organic compound between a pair of electrodes. A combination of the first organic compound and the second organic compound forms an exciplex (excited complex). An emission spectrum of the exciplex overlaps with an absorption band located on the longest wavelength side of an absorption spectrum of the phosphorescent compound. A peak wavelength of the emission spectrum of the exciplex is longer than or equal to a peak wavelength of the absorption band located on the longest wavelength side of the absorp-tion spectrum of the phosphorescent compound.