OLED Emissive Layer Using TADF Benzimidazole Emitters
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Solution Overview
Problem
Current organic electroluminescent devices (OLEDs) face limitations in achieving high internal quantum efficiency due to the spin statistics limit for fluorescent emission, and there is a need for materials that can facilitate delayed fluorescence processes, such as thermally activated delayed fluorescence (TADF), to exceed this limit.
Innovation Solution
The development of organic compounds comprising benzimidazo[1,2-a]benzimidazole moieties, which serve as emitters or hosts in OLEDs, allowing for the formation of emissive layers that incorporate electron acceptor and donor groups, potentially enabling TADF and exceeding the spin statistics limit for internal quantum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional fluorescent emitters are used in OLEDs, then the device structure is simple, but the internal quantum efficiency is limited by the spin statistics limit (25% maximum)
Solution Approach 1:
The patent changes the emission mechanism parameter from conventional fluorescence to thermally activated delayed fluorescence (TADF). This is achieved by designing emitters with small singlet-triplet energy gaps that enable reverse intersystem crossing, allowing triplet excitons to convert back to singlet states and emit photons. This parameter change enables internal quantum efficiency to exceed the traditional 25% spin statistics limit while maintaining relatively simple device structures
Solution Approach 2:
The patent employs composite material systems combining TADF emitters with specific host materials that have appropriate triplet energy levels. The host-guest system is designed so that the host has higher triplet energy than the TADF emitter, preventing triplet energy back-transfer and enabling efficient TADF emission. This composite approach resolves the contradiction by achieving high internal quantum efficiency through material composition rather than structural complexity
2Productivity
If phosphorescent emitters are used to exceed the spin statistics limit, then internal quantum efficiency improves, but device complexity and material synthesis difficulty increase
Solution Approach 1:
The patent replaces expensive, heavy metal-based phosphorescent emitters with organic TADF emitters that have longer operational lifetimes and are easier to synthesize. The TADF emitters use only light elements (C, H, N, O) and can be synthesized through standard organic synthesis methods, avoiding the need for rare earth metals and complex coordination chemistry required for phosphorescent materials
Solution Approach 2:
The patent substitutes the phosphorescence mechanism (which relies on heavy metal atoms to enhance spin-orbit coupling) with a TADF mechanism that uses thermal energy to drive reverse intersystem crossing. This substitution eliminates the need for heavy metal elements and complex photophysical processes, simplifying both material design and device fabrication while achieving comparable or superior internal quantum efficiency
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 use of these compounds in OLEDs results in external quantum efficiency exceeding theoretical limits, indicating potential TADF properties, and enhances the performance of OLEDs by achieving higher luminescent radiation output.
Implementation Method 1
there is a need for materials that can facilitate delayed fluorescence processes, such as thermally activated delayed fluorescence (TADF), to exceed this limit
Implementation Method 2
OLEDs make use of thin organic films that emit light when voltage is applied across the device
Data Source
AI summary
An OLED incorporating a first emitting compound in its emissive layer is disclosed. The first emitting compound has the formula G1-Z, Formula I, where G1 is an electron acceptor group; and Z is an electron donor group, where Z has the formula:wherein each of R1 and R2 independently represents no substitution to the maximum allowable substitution; wherein R1 and R2 are independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; and wherein two or more of R1 and R2 substitutions are optionally joined or fused into a ring.