OLED Organic Metal Complex Host for Phosphorescent Dopants
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Solution Overview
Problem
Conventional organic light emitting diodes (OLEDs) face challenges in achieving satisfactory electrical properties due to low luminous efficiency, particularly because they predominantly rely on fluorescence, which has a 25% probability of singlet excitation state, resulting in inefficient light emission.
Innovation Solution
Incorporating an oligomer-type organic metal complex as the organic layer, represented by Formula [M(L)2]a, where M is a five- or six-coordinated metal, L is an anionic ligand, and a ranges from 2-4, which acts as a host for phosphorescent dopants, enabling efficient phosphorescent emission and reducing the need for a hole blocking layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional organic light emitting diodes rely on fluorescence for light emission, then the device structure is simple, but the luminous efficiency is low due to 25% singlet excitation state probability
Solution Approach 1:
The patent changes the excitation state parameter from singlet (fluorescence) to triplet (phosphorescence) by introducing phosphorescent dopants into the organic layer, enabling the device to utilize triplet excitons for light emission and achieve internal quantum efficiency of about 100%
Solution Approach 2:
The patent introduces a hole blocking layer as an intermediary component between the emissive layer and electron transport layer, which mediates the charge distribution to create optimal conditions for phosphorescent emission by blocking holes and enhancing electron injection
2Loss of energy
If phosphorescent dopants are added to achieve high luminous efficiency, then the internal quantum efficiency improves to about 100%, but the device complexity increases due to additional layers and materials
Solution Approach 1:
The hole blocking layer serves multiple functions: it blocks holes from the emissive layer, enhances electron injection into the emissive layer, and creates the appropriate energy level alignment for efficient phosphorescent emission, thereby achieving multiple objectives with a single layer
3Ease of operation
If conventional OLEDs use fluorescence emission, then the electrical properties are easier to achieve, but the current density and lifetime are limited
Solution Approach 1:
The patent changes the emission mechanism parameter from fluorescence to phosphorescence, which fundamentally alters the electrical characteristics of the device, enabling higher current density operation and extended lifetime by utilizing triplet excitons that were previously non-emissive
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 oligomer-type organic metal complexes in OLEDs enhances electrical properties, leading to higher current density, efficiency, and longer lifetimes, while eliminating the need for a hole blocking layer, resulting in low driving voltage and improved luminescence.
Implementation Method 1
The light that is emitted when excitons drop to the ground state from a triplet excitation state is referred to as 'phosphorescence.' phosphorescence having a 25% probability of a singlet excitation state and a 75% probability of a triplet excitation state can theoretically have an internal quantum efficiency of about 100%
Implementation Method 2
When a current is applied to the anode and the cathode, electrons injected from the cathode migrate to the emissive layer via the electron transport layer. The electrons are recombined in the emissive layer with holes injected from the anode to generate excitons. When the excitons drop from an excited state to a ground state, light is emitted from the emissive layer
Data Source
AI summary
Organic light emitting diodes (OLEds) are provided. In one embodiment, an OLED includes a first electrode, a second electrode and an organic layer positioned between the first and second electrodes. The organic layer comprises an organic metal complex represented by the formula [M(L)2]a, in which L is an anionic ligand, M is a metal that can be five-coordinated or six-coordinated with L, and a is an integer ranging from 2 to 4.