Organic EL Blocking Layer Triplet Energy Alignment
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing organic electroluminescence devices face limitations in achieving high efficiency due to the inefficient utilization of triplet excitons, particularly in fluorescent emission, where the external quantum efficiency is constrained by the TTF phenomenon and the use of certain materials like BCP in blocking layers hampers the efficient generation of singlet excitons.
Innovation Solution
The introduction of a blocking layer with a specific affinity difference and triplet energy relationship between the electron injecting layer and the emitting layer, along with the use of aromatic heterocyclic derivatives and specific dopants, facilitates the TTF phenomenon, enhancing the luminous efficiency by ensuring sufficient electron supply and confining triplet excitons within the emitting layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a blocking layer with conventional materials (e.g., BCP) is used, then the device structure is simple, but the external quantum efficiency is low due to insufficient TTF phenomenon
Solution Approach 1:
The patent changes the energy level parameters of the blocking layer by selecting materials with specific triplet energy values (Et > 2.1 eV) and affinity differences (0.3-1.5 eV) relative to the electron injecting layer. This parameter optimization enables efficient TTF phenomenon while maintaining device structure simplicity, resolving the contradiction between ease of manufacture and external quantum efficiency.
Solution Approach 2:
The patent employs composite material selection by combining a blocking layer with specific aromatic heterocyclic derivatives (e.g., mCP, TCTA) and matching electron injecting layers (e.g., Alq3, BCP). This composite approach creates optimal energy level alignment for TTF phenomenon, achieving high external quantum efficiency without complicating the overall device structure.
2Speed
If the affinity difference between electron injecting layer and blocking layer is large, then electron injection is facilitated, but triplet excitons cannot be confined in the emitting layer, reducing singlet exciton generation
Solution Approach 1:
The patent optimizes the affinity difference parameter to a specific range (0.3-1.5 eV) rather than maximizing it. This controlled parameter change ensures sufficient electron injection while maintaining triplet exciton confinement in the emitting layer, enabling efficient TTF phenomenon and singlet exciton generation.
Solution Approach 2:
The patent applies local quality by creating distinct energy level characteristics in different layers: the blocking layer has higher triplet energy than the emitting layer to confine triplet excitons, while the affinity difference is controlled to allow electron injection. This localized optimization of energy levels resolves the contradiction between electron injection and triplet exciton confinement.
3Device complexity
If triplet excitons are not effectively utilized, then the device operation is simple, but the luminous efficiency is limited to 25% theoretical maximum
Solution Approach 1:
The patent converts the previously harmful or wasted triplet excitons into beneficial singlet excitons through the TTF phenomenon. By designing the blocking layer with appropriate triplet energy, triplet excitons that would normally be lost are now utilized to generate singlet excitons that contribute to fluorescent emission, achieving internal quantum efficiency exceeding 25% while maintaining fluorescent device simplicity.
Solution Approach 2:
The blocking layer serves as an intermediary that mediates the interaction between triplet excitons and the electron injecting layer. It provides the energy level alignment necessary for TTF phenomenon to occur, enabling efficient conversion of triplet excitons to singlet excitons without complicating the overall fluorescent emission 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
This configuration significantly improves the external quantum efficiency by effectively generating singlet excitons through triplet exciton collisions, leading to enhanced luminous intensity and efficiency in organic electroluminescence devices.
Implementation Method 1
A mechanism is found that singlet excitons are generated by collision and fusion of two triplet excitons, whereby fluorescent emission is increased. Such a phenomenon in which singlet excitons are generated by collision and fusion of two triplet excitons is hereinafter referred to as TTF (Triplet-Triplet Fusion) phenomenon.
Implementation Method 2
An organic electroluminescence device (hereinafter, referred to as organic EL device)
Data Source
Figure 1
Figure 2
Figure 3
AI summary
An organic electroluminescence device (1) includes an anode (10), an emitting layer (20), a blocking layer (30), an electron injecting layer (40), and a cathode (50) in sequential order. The emitting layer (20) includes a host and dopant. The blocking layer (30) includes an aromatic heterocyclic derivative. A triplet energy ET b (eV) of the blocking layer (30) is larger than a triplet energy ET h (eV) of the host. An affinity Ab (eV) of the blocking layer (30) and an affinity Ae (eV) of the electron injecting layer satisfy a relationship of Ae-Ab<0.2.