Light Emitting Element with Intermediate Layer for Roll-off Reduction
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Solution Overview
Problem
Existing light emitting elements for display devices face challenges in achieving high efficiency and stability, particularly in maintaining light efficiency and preventing roll-off characteristics over various grayscale levels.
Innovation Solution
A light emitting element is designed with a specific structure that includes an anode electrode, a cathode electrode, and a light emitting structure comprising a first light emitting unit, a charge generation layer, and a second light emitting unit. The second light emitting unit includes multiple layers such as a second hole transport unit, a second light emitting layer, an intermediate layer, a third light emitting layer, and a second electron transport unit, optimized to manage electron and hole injection and emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a conventional light emitting element structure is used, then the device complexity is low, but the light efficiency is insufficient and roll-off characteristics occur
Solution Approach 1:
The light emitting element is divided into multiple light emitting units (first light emitting unit with first light emitting layer emitting blue light, second light emitting unit with second and third light emitting layers emitting red and green light respectively). Each unit has its own hole transport unit, light emitting layer(s), and electron transport unit, allowing independent optimization of each color channel to improve overall light efficiency while managing complexity through modular design
Solution Approach 2:
The patent introduces an intermediate layer between the second light emitting layer and third light emitting layer, creating a multi-dimensional energy level structure. The intermediate layer has a LUMO energy level higher than the third light emitting layer but less than 1.5 eV, which adds an energy dimension to control electron transport and reduce roll-off effects across different grayscale levels
2Illumination intensity
If the light emitting layer thickness is increased to improve light output, then the light efficiency improves, but the roll-off phenomenon worsens at high grayscale levels
Solution Approach 1:
Different light emitting layers have optimized local properties: the first light emitting layer (blue) has specific thickness for blue light emission, the second light emitting layer (red) is optimized for red emission, and the third light emitting layer (green) is optimized for green emission. The intermediate layer with specific LUMO energy level (higher than third light emitting layer but less than 1.5 eV) provides localized electron transport control to prevent exciton accumulation and reduce roll-off at high grayscale levels
Solution Approach 2:
The patent optimizes the thickness parameters of each light emitting layer and the intermediate layer to achieve the right balance. The total thickness of second light emitting layer, intermediate layer, and third light emitting layer is controlled at 300-500 Å, with the intermediate layer specifically at 5-30 Å. These parameter optimizations ensure sufficient light output while maintaining stable performance across grayscale levels by controlling electron-hole recombination efficiency
3Productivity
If multiple light emitting layers are added to improve color performance, then the light efficiency improves, but the manufacturing precision requirements increase
Solution Approach 1:
The device is segmented into discrete functional layers with clear interfaces: hole transport units, light emitting layers (first, second, third), intermediate layer, and electron transport units. Each layer has a defined thickness range and material composition, which simplifies the manufacturing process by providing clear fabrication targets for each layer while achieving superior color performance through the multi-layer structure
Solution Approach 2:
The patent specifies precise parameter ranges for manufacturing: total thickness of 300-500 Å for the combined second light emitting layer, intermediate layer, and third light emitting layer, with the intermediate layer at 5-30 Å. These parameter specifications provide clear manufacturing guidance while ensuring optimal performance, reducing the burden of precision control by defining acceptable ranges rather than single values
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 light efficiency and reduces roll-off phenomena by controlling the distribution of excitons across different light emitting layers, thereby maintaining high performance across various grayscale levels without significant increases in driving voltage.
Implementation Method 1
The light emitting element may be to emit light, for example, when a hole from an anode electrode and an electron injected from a cathode electrode in a light emitting layer recombine to generate an exciton, which transitions (e.g., relaxes, from an excited state to a ground state) to emit light
Data Source
AI summary
A light emitting element includes an anode electrode, a cathode electrode facing the anode electrode, and a light emitting structure provided between the anode electrode and the cathode electrode, and including a first light emitting unit, a charge generation layer, and a second light emitting unit. The second light emitting unit includes a second hole transport unit provided on the charge generation layer, a second light emitting layer provided on the second hole transport unit, an intermediate layer provided on the second light emitting layer, a third light emitting layer provided on the intermediate layer, and a second electron transport unit provided between the third light emitting layer and the cathode electrode.