Organic Light Emitting Device Triplet Harvesting Complex
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Solution Overview
Problem
Organic light-emitting diodes (OLEDs) face limitations in electroluminescence efficiency due to the 25% maximum efficiency constraint from singlet and triplet exciton formation, and thermally activated delayed fluorescence (TADF) materials suffer from long delayed fluorescence lifetimes leading to poor device stability and roll-off.
Innovation Solution
An organic light-emitting device comprising an emissive layer with a first organic semiconductor compound having a spin singlet ground state and a second compound with a spin doublet ground state, where energy is transferred from spin singlet and triplet excited states to create spin doublet excited states, enabling efficient fluorescent light emission with reduced lifetimes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If TADF materials are used to improve electroluminescence efficiency by harvesting triplet excitons, then efficiency is improved, but delayed fluorescence lifetime becomes long (microseconds and longer) leading to poor device stability and roll-off
Solution Approach 1:
The patent introduces a triplet harvesting complex (THC) as an intermediary component in the emissive layer. The THC accepts triplet excitons from the TADF emitter through triplet-triplet energy transfer, converting them into singlet excitons on the THC, which then transfer energy to the phosphorescent dopant for light emission. This mediator approach allows efficient triplet harvesting while avoiding the long-lived delayed fluorescence state that causes stability issues.
Solution Approach 2:
The patent changes the emission mechanism parameters by introducing a phosphorescent dopant (iridium complex) with long phosphorescent lifetime that can efficiently receive energy from the THC. This parameter change in the emission pathway allows the system to bypass the problematic long-lived TADF state while maintaining high efficiency through the phosphorescent emission channel with appropriate lifetime characteristics.
2Use of energy by moving object
If TADF materials are used to harvest both singlet and triplet excitons, then electroluminescence efficiency exceeds 25%, but roll-off increases and operational life decreases
Solution Approach 1:
The THC acts as an intermediary that receives triplet excitons from the TADF emitter and transfers them to the phosphorescent dopant. This intermediary mechanism enables the system to harvest both singlet and triplet excitons efficiently (achieving >25% electroluminescence efficiency) while the phosphorescent emission pathway provides stable, long-duration operation, extending operational life.
3Device complexity
If conventional closed-shell molecules are used, then device structure is simple, but electroluminescence efficiency is limited to maximum 25% due to singlet and triplet exciton formation
Solution Approach 1:
The patent employs a composite emissive layer containing four distinct components: TADF emitter molecules, triplet harvesting complex (THC) molecules, phosphorescent dopant (iridium complex), and host matrix material. This composite structure enables efficient harvesting of both singlet and triplet excitons while maintaining manageable device complexity through systematic material integration.
Solution Approach 2:
The THC serves as an intermediary component that facilitates efficient energy transfer from triplet excitons to the phosphorescent dopant. This intermediary mechanism allows the composite system to overcome the 25% efficiency limit of conventional closed-shell molecules by providing dedicated pathways for both singlet and triplet exciton utilization.
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 achieves enhanced electroluminescence efficiency and improved stability by harvesting energy from both singlet and triplet excitons, reducing roll-off and extending device operational life.
Implementation Method 1
energy is transferred from spin singlet and triplet excited states to create spin doublet excited states
Implementation Method 2
enabling efficient fluorescent light emission with reduced lifetimes
Implementation Method 3
enhanced electroluminescence efficiency by harvesting energy from both singlet and triplet excitons
Data Source
AI summary
An organic light emitting device, comprising an anode; a cathode; and an emissive layer between the anode and the cathode, wherein the emissive layer comprises a first material which is an organic semiconductor compound and a second material which is a different organic semiconductor compound that has a spin doublet ground state; and wherein a lowest spin singlet excitation energy of the first material and a lowest spin triplet excitation energy of the first material are greater than a lowest spin doublet excitation energy of the second material; a method of fabricating an organic light emitting device, comprising: forming an emissive layer between an anode and a cathode, wherein the emissive layer comprises a first material which is an organic semiconductor compound and a second material which is a different organic semiconductor compound that has a spin doublet ground state; and wherein a lowest spin singlet excitation energy of the first material and a lowest spin triplet excitation energy of the first material are greater than a lowest spin doublet excitation energy of the second material; and a method of operating the device by applying a voltage across the device, such that spin singlet excited states and spin triplet excited states are formed for the first material, wherein energy is transferred from spin singlet excited states in the first material and spin triplet excited states in the first material to form spin doublet excited states in the second material, wherein the second material emits fluorescent light when transitioning from a spin doublet excited state to a ground state.