Phosphorescent OLED Emitter with Coumarin Ligands
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Solution Overview
Problem
Existing organic electroluminescent (EL) devices face limitations in drive voltage, luminance, and efficiency due to the inefficiency in utilizing triplet excitons, which are not readily converted to light emission, and there is a need for improved phosphorescent dopants to enhance performance.
Innovation Solution
The development of OLED devices incorporating a phosphorescent emitter represented by Formula (I) with cyclometallated ligands containing a coumarin group, where M is Ir or Pt, to improve drive voltage, luminance, and efficiency, and the use of specific compounds as dopants to facilitate energy transfer from both singlet and triplet excitons.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional fluorescent emitting materials are used in OLED devices, then the device structure is simple, but only 25% of excitons (singlet excitons) can be utilized for light emission resulting in low efficiency
Solution Approach 1:
The patent changes the emission mechanism parameter from fluorescence to phosphorescence by introducing phosphorescent dopants with triplet excited states. This allows utilization of both singlet and triplet excitons for light emission, dramatically improving efficiency from 25% to potentially 100% exciton utilization.
Solution Approach 2:
The patent employs composite material systems consisting of host materials doped with phosphorescent guest materials (iridium or platinum complexes). This composite approach enables efficient energy transfer from both singlet and triplet excitons to the phosphorescent dopant, achieving high efficiency while maintaining device functionality.
2Productivity
If phosphorescent dopants are introduced to utilize triplet excitons, then light emission efficiency improves, but device complexity increases due to additional material requirements
Solution Approach 1:
The patent introduces host materials as intermediaries that facilitate energy transfer from excitons to phosphorescent dopants. The host materials create a favorable environment for phosphorescence by providing appropriate energy levels and protecting the sensitive phosphorescent complexes, thus enabling efficient triplet exciton utilization without directly complicating the device structure.
3Device complexity
If early organic EL devices with thick organic layers are used, then device structure is simple, but operating voltage is very high (>100V)
Solution Approach 1:
The patent changes the organic layer thickness parameter from micrometer scale (>1 μm) to nanometer scale (few nanometers). This dramatic reduction in thickness, combined with the use of phosphorescent materials, enables efficient charge recombination and light emission at much lower operating voltages, resolving the contradiction between structural simplicity and energy consumption.
4Ease of manufacture
If conventional organic EL devices are used, then manufacturing is straightforward, but luminance and efficiency are limited
Solution Approach 1:
The patent changes the emission mechanism parameter from fluorescence to phosphorescence, which fundamentally improves luminance and efficiency. The phosphorescent materials enable utilization of both singlet and triplet excitons, producing significantly higher light output and device efficiency while maintaining compatibility with conventional OLED manufacturing processes.
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 OLED devices with improved drive voltage, luminance, and efficiency, enabling more effective energy transfer and enhanced light emission by utilizing both singlet and triplet excitons, thereby overcoming the limitations of previous devices.
Implementation Method 1
If the triplet state of the dopant is emissive it can produce light by phosphorescence
Implementation Method 2
The excited singlet state is created when excitons formed in an OLED device transfer their energy to the excited state of the dopant
Implementation Method 3
The singlet excited state can often relax, by an intersystem crossing process, to the emissive triplet excited state
Data Source
AI summary
An OLED device comprises a cathode, an anode, and has therebetween a light emitting layer comprising a phosphorescent emitter represented by Formula (I):LnM (I)wherein each L is a cyclometallated ligand with at least one containing a coumarin group, M is Ir or Pt, and n is 3 when M is Ir and 2 when M is Pt. The invention also comprised the compound of formula (I).