OLED Emission Layer Compounds for Large-ΔEST TADF
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Solution Overview
Problem
Current organic light-emitting devices (OLEDs) face limitations in achieving efficient thermally activated delayed fluorescence (TADF) with compounds having relatively large ΔEST values, which affects their light-emission characteristics and efficiency.
Innovation Solution
Incorporating a compound that satisfies specific conditions regarding excitation energy levels, including ΔEST > ΔEST2 + ΔE′TT, 0 eV < ΔEST2 + ΔE′TT ≤ 1.0 eV, 0 eV < ΔE′TT ≤ 0.15 eV, and ΔEST2 > 0 eV, to enable TADF even when ΔEST is greater than 0.2 eV, thereby improving the efficiency and lifespan of OLEDs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a compound with relatively large ΔEST value is used in the emission layer, then the device can achieve TADF, but the light-emission efficiency and lifespan are reduced
Solution Approach 1:
The patent applies parameter changes by precisely controlling the excitation energy levels (ΔEST, ΔEST2, ΔE′TT) of the compound in the emission layer. By satisfying specific mathematical relationships between these energy parameters, the device achieves TADF with improved efficiency and lifespan, transforming the qualitative observation into a quantitative design rule.
Solution Approach 2:
The patent employs composite materials by combining the TADF compound with appropriate host materials in the emission layer. This composite structure enables efficient energy transfer from the host to the TADF compound while maintaining device stability and lifespan, resolving the contradiction between achieving TADF and maintaining reliability.
2Use of energy by moving object
If a compound with large ΔEST value is used, then TADF can be achieved, but the driving voltage increases
Solution Approach 1:
The patent uses parameter changes by optimizing the energy level parameters (ΔEST, ΔEST2, ΔE′TT) to achieve TADF with favorable voltage characteristics. By controlling these parameters within specific ranges, the device achieves high luminescence efficiency without excessive driving voltage, resolving the contradiction between efficiency and voltage.
3Device complexity
If conventional emission layer materials are used, then the device structure is simple, but energy transfer efficiency is low
Solution Approach 1:
The patent applies parameter changes by selecting compounds with specific energy level parameters (ΔEST > ΔEST2 + ΔE′TT, 0 eV < ΔEST2 + ΔE′TT ≤ 1.0 eV, 0 eV < ΔE′TT ≤ 0.15 eV) that enable efficient energy transfer. This maintains a relatively simple emission layer structure while dramatically improving energy transfer efficiency through the special energy level matching.
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 compound enables OLEDs to emit thermally activated delayed fluorescence, enhancing light-emission characteristics and efficiency without increasing driving voltage, and improves energy transfer and exciton lifespan, leading to improved luminescence and durability.
Implementation Method 1
enabling TADF even when ΔEST is greater than 0.2 eV, and using it as a fluorescence emitter or sensitizer to enhance energy transfer and luminescence efficiency
Implementation Method 2
ΔEST indicates a difference between a lowest singlet excitation energy level calculated for an S1 equilibrium structure of the compound and a lowest triplet excitation energy level calculated for a T1 equilibrium structure of the compound
Implementation Method 3
The holes and the electrons recombine in the emission layer to produce excitons. These excitons may transition from an excited state to a ground state, thereby generating light
Data Source
AI summary
Disclosed is an organic light-emitting device including an emission layer that includes a compound.