White Organic EL Element Hole-Blocking Layer Design
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Solution Overview
Problem
White organic EL elements face issues with high drive voltage and insufficient durability due to the tandem structure and instability of nitrogen-containing heterocyclic compounds used in the electron supply layer, which affects the overall performance and longevity of the device.
Innovation Solution
A white organic EL element is designed with a specific layer structure comprising a blue-light-emitting layer, a hole-blocking layer formed of hydrocarbon, and an electron transport layer made of a nitrogen-containing heterocyclic compound, where the hole-blocking layer is thicker than the electron transport layer, and the layers are optimized to satisfy specific thickness and energy level relationships to enhance durability and reduce drive voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a tandem structure with charge generation layer is used, then current leakage is reduced, but drive voltage increases
Solution Approach 1:
The patent removes the charge generation layer from the tandem structure, simplifying the device architecture. This extraction eliminates the high-voltage requirement associated with charge generation layers while maintaining current leakage reduction through alternative means (optimized electron supply layer and hole-blocking layer configuration).
Solution Approach 2:
The patent divides the electron supply function into two separate layers: an electron transport layer (with nitrogen-containing heterocyclic compound) and a hole-blocking layer (adjacent to light-emitting layer). This segmentation allows each layer to be optimized for its specific function, reducing overall drive voltage while preventing current leakage.
2Reliability
If electron supply layer is made thick, then current leakage is reduced, but element thickness increases and voltage increases
Solution Approach 1:
The electron supply function is segmented into two thin layers (electron transport layer and hole-blocking layer) rather than using one thick layer. This segmentation achieves the same current leakage prevention function while minimizing total thickness and maintaining low drive voltage.
Solution Approach 2:
Each layer is designed with specific local properties: the electron transport layer has high electron mobility to transport electrons efficiently, while the hole-blocking layer has properties that prevent hole penetration. This localized optimization allows thin layers to achieve functions that would otherwise require thick layers.
3Ease of operation
If nitrogen-containing heterocyclic compound is used in electron supply layer adjacent to light-emitting layer, then carrier balance is adjusted, but durability decreases due to material instability
Solution Approach 1:
The patent segments the electron supply layer into two distinct layers with different material compositions. The nitrogen-containing heterocyclic compound is confined to the electron transport layer (away from the light-emitting layer), while the hole-blocking layer uses more stable materials. This segmentation protects the unstable nitrogen-containing compound from direct contact with holes, improving durability while maintaining carrier balance.
Solution Approach 2:
The hole-blocking layer acts as an intermediary barrier between the nitrogen-containing heterocyclic compound and the holes from the light-emitting layer. This intermediary prevents direct interaction that would cause deterioration, thereby extending device lifetime while still allowing the electron transport layer to perform its carrier balance function.
4Illumination intensity
If amine compound is used as luminescent material in light-emitting layer, then light emission is achieved, but hole-trapping properties cause interaction with nitrogen-containing heterocyclic compound forming hole-blocking layer
Solution Approach 1:
The patent extracts the hole-blocking function from the nitrogen-containing heterocyclic compound by introducing a dedicated hole-blocking layer. This separation prevents the harmful interaction between holes (trapped by amine compound) and the nitrogen-containing compound, eliminating the formation of unstable hole-blocking complexes while preserving light emission from the amine compound.
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 results in a white organic EL element with improved voltage properties and increased durability, achieving efficient white-light emission and prolonged device lifespan by localizing recombination regions and preventing material deterioration.
Implementation Method 1
a first dopant that emits blue fluorescent light
Data Source
AI summary
A white organic electroluminescent (EL) element includes, in sequence, an anode, a first light-emitting layer that is a blue-light-emitting layer, a hole-blocking layer, an electron transport layer, and a cathode. The hole-blocking layer is adjacent to the first light-emitting layer and the electron transport layer and formed of a hydrocarbon. The electron transport layer is formed of a nitrogen-containing heterocyclic compound. The first light-emitting layer contains a first host and a first dopant that emits blue fluorescent light. Relations (a), (b), and (c) are satisfied.LUMO(H1)>LUMO(D1) (a)0.1<d(ETL)/d(HBL)<0.7 (b)90 nm≤d(E)=d(HBL)+d(ETL)<150 nm (c)LUMO (H1): lowest unoccupied molecular orbital (LUMO) energy of first hostLUMO (D1): LUMO energy of first dopantd (HBL): thickness of hole-blocking layerd (ETL): thickness of electron transport layer.