OLED Emission Layer Structure for Exciton Confinement at Low Voltage
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Solution Overview
Problem
Existing organic light emitting display devices face inefficiencies due to high driving voltages and low hole mobility in hole transport layers with high triplet energy levels, leading to increased recombination areas and reduced emission efficiency.
Innovation Solution
The device incorporates a first emission part with a first hole transport layer thickness of 20 nm or less and an electron blocking layer with a thickness greater than the hole transport layer, having a triplet energy level of 2.7 eV to 2.9 eV, to enhance exciton confinement and reduce driving voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a hole transport layer with high triplet energy level is used to enhance emission efficiency, then exciton confinement is improved, but hole mobility decreases and driving voltage increases
Solution Approach 1:
The hole transport layer is divided into multiple sub-layers with different thicknesses and triplet energy levels. The first hole transport layer has higher triplet energy level to confine excitons, while the second hole transport layer has lower triplet energy level to facilitate hole transport, thus resolving the contradiction between exciton confinement and hole mobility
Solution Approach 2:
Different regions of the hole transport layer are assigned different properties: the region closer to the emission layer has higher triplet energy level for exciton confinement, while the region closer to the electrode has lower triplet energy level for better hole mobility, achieving local optimization of both functions
2Productivity
If the thickness of the hole transport layer is increased to improve exciton confinement, then emission efficiency is enhanced, but the recombination area increases and driving voltage rises
Solution Approach 1:
The hole transport layer is segmented into multiple thin sub-layers instead of one thick layer. This segmentation maintains adequate exciton confinement while reducing the total recombination area and keeping the driving voltage low
Solution Approach 2:
Instead of using a uniformly thick hole transport layer, the invention uses multiple thinner layers with cumulative thickness optimized for exciton confinement, achieving sufficient emission efficiency without excessive recombination area
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
This configuration enhances emission efficiency by maximizing exciton confinement and maintaining low driving voltage, while potentially reducing manufacturing costs through shared processes with bottom emission type displays.
Implementation Method 1
an exciton is generated by combining the electron with the hole. The organic light emitting device is a device using the principle that light is emitted when the generated exciton is dropped from an excited state to a ground state
Implementation Method 2
The fluorescence emission layer may use the principle that light is emitted when an exciton is dropped from a singlet excited state to a ground state
Implementation Method 3
the phosphorescence emission layer may use the principle that light is emitted when the exciton is dropped from a triplet excited state to the ground state
Data Source
AI summary
Disclosed is an organic light emitting display device. The organic light emitting display device includes a first emission part between a first electrode and a second electrode and a second emission part on the first emission part. The first emission part includes a first hole transport layer and a first emission layer, and the second emission part includes a second hole transport layer and a second emission layer. A thickness of the second hole transport layer is greater than a thickness of the first hole transport layer.