Cross-linkable Triarylamine Polymer for OLED Efficiency
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Solution Overview
Problem
Existing organic electroluminescent elements face issues with high operating voltage, low light-emitting efficiency, and short drivable life due to the reduction in charge transporting ability and oxidation-reduction stability when polymers with rigid main chains undergo cross-linking, and the difficulty in forming multiple layers using triarylamine-containing polymers without cross-linkable groups.
Innovation Solution
A polymer with a specific structure containing an alkylene group (quaternary carbon) and a cross-linkable group is developed, allowing for the formation of multiple layers by becoming insoluble in organic solvents, maintaining high charge transporting ability and electrochemical stability, and enabling the creation of organic electroluminescent elements with high excited singlet and triplet levels, low operating voltage, and improved light-emitting efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If polymers with rigid main chains undergo cross-linking to form network polymer, then multiple layers can be formed by becoming insoluble in organic solvents, but charge transporting ability and oxidation-reduction stability are seriously reduced
Solution Approach 1:
The patent applies local quality by introducing flexible alkylene groups (containing quaternary carbon atoms) at specific positions within the polymer chain, while maintaining rigid aromatic main chains for overall structural stability. This localized flexibility prevents excessive aggregation and maintains charge transporting ability even after cross-linking, resolving the contradiction between insolubility and charge transport.
Solution Approach 2:
The patent creates a composite structure by combining rigid aromatic rings (for stability and insolubility) with flexible alkylene chains (for charge transport). The repeating unit contains both rigid and flexible components, forming a composite polymer that achieves both multiple-layer formation capability and maintained charge transporting ability after cross-linking.
2Stability of the object's composition
If polymers with rigid main chains undergo cross-linking, then multiple layers can be formed, but light-emitting efficiency is reduced due to formation of J-aggregate
Solution Approach 1:
The flexible alkylene groups are strategically positioned within the repeating unit to locally disrupt π-conjugation system aggregation. This localized modification prevents the formation of J-aggregates that would otherwise cause energy loss, while the overall rigid structure maintains insolubility for multiple-layer formation.
Solution Approach 2:
The patent changes the structural parameters of the polymer by introducing alkylene groups with specific chain lengths and quaternary carbon atoms. This parameter modification alters the aggregation behavior of the polymer chains, preventing harmful J-aggregate formation while maintaining the desired insolubility and light-emitting efficiency.
3Reliability
If triarylamine-containing polymer without cross-linkable groups is used, then charge transporting ability is maintained, but formation of multiple layers is difficult
Solution Approach 1:
The patent merges two previously separate functions into a single polymer structure: the triarylamine group (providing charge transporting ability) and the cross-linkable group (enabling multiple-layer formation). This combination allows the polymer to simultaneously maintain charge transport while becoming insoluble after cross-linking for multi-layer device fabrication.
Solution Approach 2:
The repeating unit is designed with multi-functionality, containing both hole-transporting triarylamine moieties and cross-linkable groups. This universal structure performs multiple functions: charge transport, structural stability, and enablement of multi-layer formation, eliminating the need for separate materials for each function.
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 polymer enables the formation of organic electroluminescent elements with high light-emitting efficiency, low voltage operation, and enhanced driving stability, facilitating the creation of display and lighting devices with improved performance.
Implementation Method 1
a polymer having a weight-average molecular weight (Mw) of 20,000 or more and a degree of dispersion (Mw/Mn) of 2.5 or less and comprising a repeating unit represented by the following general formula (1) and a cross-linkable group
Implementation Method 2
having a high hole transporting ability and a high electrochemical stability
Implementation Method 3
enables formation of multiple layers by the wet film formation method, shows a high excited singlet level and a high excited triplet level after being made insoluble in an organic solvent by cross-linking
Data Source
Figure 1
AI summary
An object of the present invention is to provide a polymer which shows a high excited singlet level and a high excited triplet level, which has excellent charge transporting ability and excellent electrochemical stability, which enables formation of multiple layers, which is scarcely decomposed, and which can provide a uniform film quality, and to provide an organic electroluminescent element material and an organic electroluminescent element composition, and to provide an organic electroluminescent element which shows a high light-emitting efficiency and drivability at a low voltage and a high driving stability, and a display device and a lighting device. The present invention relates to a polymer comprising a repeating unit represented by the following general formula (1) and a cross-linkable group (wherein Ar11 to Ar13 each independently represents a divalent aromatic group which may have a substituent, Ar14 and Ar15 each independently represents an aromatic group which may have a substituent, Ar16 and Ar17 each independently represents a direct bond or a divalent aromatic group which may have a substituent, R11 and R12 each independently represents a hydrogen atom, an alkyl group which may have a substituent, an alkoxy group which may have a substituent, or an aromatic group which may have a substituent, r represents an integer of from 0 to 5, and R11 and R12 may be connected to each other to form a ring structure, in which the repeating unit represented by the above-described general formula (1) may contain the cross-linking group):