Organic Electroluminescence Device Using TADF and Fused Ring Host
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Solution Overview
Problem
Conventional organic electroluminescence devices face limitations in achieving high performance due to the inefficient utilization of triplet excitons, which are typically lost as heat, leading to reduced efficiency and shorter device lifetimes.
Innovation Solution
Incorporating a delayed fluorescent compound and a second aromatic hydrocarbon compound with a fused ring structure in the emitting layer, where the delayed fluorescent compound undergoes thermally activated delayed fluorescence (TADF) and energy transfer occurs to the second compound, enhancing internal quantum efficiency and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a fluorescent organic EL device is used, then the device can be applied to full-color displays, but the internal quantum efficiency is limited due to loss of triplet excitons
Solution Approach 1:
The patent converts the harmful loss of triplet excitons (which normally decay non-radiatively) into a beneficial effect by using TADF materials. The triplet excitons are converted back to singlet excitons through thermal energy, which then emit light radiatively. This transforms the previously wasted triplet state into a useful light-emitting state, achieving internal quantum efficiency approaching 100%.
Solution Approach 2:
The patent changes the energy level parameters of the emitting layer by selecting TADF materials with specific singlet-triplet energy gaps (ΔEST < 2.5 eV). This parameter change enables efficient inverse intersystem crossing from triplet to singlet state, allowing triplet excitons to contribute to light emission and thereby improving internal quantum efficiency.
2Reliability
If conventional fluorescent materials are used, then the device structure is simple, but the device lifetime is short due to low excitation stability
Solution Approach 1:
The patent employs composite material strategy by combining TADF emitters with specific host materials (formula (2) compounds with fused ring structures). This composite system provides both high excitation stability for extended device lifetime and the necessary TADF mechanism for high efficiency, while maintaining manageable device structure.
Solution Approach 2:
The patent applies local quality principle by selecting host materials with specific structural features (fused ring structures) that provide high excitation stability locally in the emitting layer. This localized optimization of material properties enhances overall device reliability without requiring complete redesign of the entire device structure.
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
This configuration significantly improves the internal quantum efficiency and extends the lifetime of the organic electroluminescence device by effectively utilizing triplet excitons through the TADF mechanism and maintaining high excitation stability.
Implementation Method 1
a thermally activated delayed fluorescence (TADF) mechanism has been studied. The TADF mechanism uses such a phenomenon that inverse intersystem crossing from triplet excitons to singlet excitons thermally occurs when a material having a small energy difference (ΔST) between singlet energy level and triplet energy level is used.
Implementation Method 2
Incorporating a delayed fluorescent compound and a second aromatic hydrocarbon compound with a fused ring structure in the emitting layer, where the delayed fluorescent compound undergoes thermally activated delayed fluorescence (TADF) and energy transfer occurs to the second compound
Data Source
AI summary
An object of the invention is to provide a high-performance organic electroluminescence device and an electronic device including the organic electroluminescence device. An organic electroluminescence device includes an anode, a cathode and an emitting layer, in which the emitting layer includes a first compound and a second compound, the first compound is a delayed fluorescent compound, and the second compound is represented by a formula (2) below.