TADF Emitters for OLEDs Using Phthalimide Hosts
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional organic light-emitting diodes (OLEDs) face inefficiencies in exciton utilization, as phosphorescent materials rely on rare and expensive metals, and fluorescent materials can only harvest singlet excitons, limiting their electroluminescent efficiency.
Innovation Solution
Development of thermally activated delayed fluorescence (TADF) emitters and hosts based on phthalimide and naphthalimide compounds with a small energy gap between S1 and T1 states, enabling the up-conversion of triplet excitons to singlet excitons, thereby enhancing exciton utilization efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If phosphorescent materials are used to harvest triplet excitons, then electroluminescent efficiency is improved, but device complexity and material cost increase due to reliance on rare metals like Ir or Pt
Solution Approach 1:
The patent extracts the essential function of phosphorescent materials (triplet exciton harvesting) and implements it through a different mechanism - TADF emitters that utilize thermal energy to convert triplet excitons to singlet excitons, thereby eliminating the need for rare metal elements while maintaining high electroluminescent efficiency
Solution Approach 2:
The patent changes the energy gap parameter (ΔEST) between S1 and T1 states to be sufficiently small, enabling thermal up-conversion of triplet excitons to singlet excitons. This parameter change allows the system to achieve phosphorescent-like efficiency without requiring phosphorescent materials containing rare metals
2Device complexity
If fluorescent materials are used for light emission, then device simplicity is maintained, but exciton utilization efficiency deteriorates because only singlet excitons (25%) can be harvested
Solution Approach 1:
The patent implements continuous useful action by enabling the system to utilize both singlet and triplet excitons for light emission. Through TADF mechanism, triplet excitons are continuously converted to singlet excitons via thermal energy, allowing all generated excitons to contribute to light emission rather than losing 75% as non-emissive triplet states
Solution Approach 2:
The patent introduces thermal energy as an intermediary that mediates the conversion between triplet and singlet excitons. The small energy gap (ΔEST) acts as an intermediary parameter that enables thermal up-conversion, bridging the gap between triplet and singlet states and allowing indirect utilization of triplet excitons through the thermal mediation process
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 TADF emitters and hosts in OLEDs achieves high electroluminescent efficiency with external quantum efficiency exceeding 5% and reduced efficiency roll-off at high luminance, utilizing all excitons for light production through singlet decay.
Implementation Method 1
thermally activated delayed fluorescence (TADF) emitters and/or hosts on basis of phthalimide and naphthalimide, which have a sufficiently small energy gap between S1 and T1 (ΔEST) to enable up-conversion of the triplet exciton from T1 to S1
Implementation Method 2
The organic light emitting elements show high electroluminescent efficiency
Data Source
AI summary
The present invention relates to organic light emitting elements, comprising thermally activated delayed fluorescence (TADF) emitters and/or hosts on basis of phthalimide and naphthalimide materials, which have a sufficiently small energy gap between S1 and T1 (ΔEST) to enable up-conversion of the triplet exciton from T1 to S1. The organic light emitting elements show high electroluminescent efficiency.