OLED Light-Emitting Layer Exciplex Tuning for Lower Drive Voltage
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Solution Overview
Problem
Organic electroluminescence (EL) elements face limitations in external quantum efficiency and drive voltage, with conventional light-emitting elements achieving only up to 20% external quantum efficiency and higher drive voltages due to inefficiencies in energy transfer from the host material to the phosphorescent compound, particularly from the singlet excited state.
Innovation Solution
A light-emitting element is designed with a phosphorescent compound, a first organic compound, and a second organic compound forming an exciplex, where the exciplex's emission spectrum overlaps with the absorption band of the phosphorescent compound on the longest wavelength side, enabling efficient energy transfer and reducing drive voltage by optimizing the peak wavelength of the exciplex emission to match or exceed the phosphorescent compound's absorption.
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 comprising a first organic compound and a second organic compound as an intermediary energy transfer medium. The exciplex absorbs energy from the phosphorescent compound and re-emits at a longer wavelength that better matches the absorption characteristics of the phosphorescent compound, creating an efficient energy transfer pathway that overcomes the light extraction limitation
Solution Approach 2:
The patent optimizes the energy level parameters of the exciplex system by selecting organic compounds with specific HOMO and LUMO levels. The exciplex emission spectrum is engineered to overlap with the absorption band of the phosphorescent compound on the longest wavelength side, and the peak wavelength of exciplex emission is set to be longer than or equal to the peak wavelength of the phosphorescent compound absorption, maximizing energy transfer efficiency
2Reliability
If the phosphorescent compound is dispersed in a host material matrix to suppress concentration quenching, then emission efficiency improves, but energy transfer efficiency from host to phosphorescent compound remains insufficient
Solution Approach 1:
The patent creates a composite light-emitting layer containing the phosphorescent compound, first organic compound, and second organic compound. This composite structure enables the exciplex system to mediate energy transfer from the host material to the phosphorescent compound, achieving both suppression of concentration quenching through dispersion and high energy transfer efficiency through the exciplex mechanism
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 approach achieves high external quantum efficiency exceeding conventional limits, up to 27%, and reduces drive voltage requirements, enhancing power efficiency and emission efficiency while minimizing energy deactivation through the exciplex-mediated energy transfer.
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 absorption spectrum of the phosphorescent compound.