Dual Light Emitting Layer Quantum Dot Device
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Solution Overview
Problem
Quantum dot electroluminescent devices face issues with inconsistent hole flow and exciton trapping due to energy level mismatches at the hole transport layer and light emitting layer interfaces, leading to reduced luminous efficiency and device degradation.
Innovation Solution
A dual light emitting layer structure with a first light emitting layer containing quantum dots and a p-type organic semiconductor, and a second light emitting layer with an n-type organic semiconductor, where the n-type organic semiconductor has a HOMO energy level ≤ -7.0 eV and the p-type organic semiconductor has a LUMO energy level ≥ -3.0 eV, is used to stabilize the hole-electron balance and confine excitons within the light emitting layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single light emitting layer with quantum dots is used, then the device structure is simple, but exciton confinement is poor leading to reduced luminous efficiency
Solution Approach 1:
The light emitting layer is segmented into two distinct layers: a first light emitting layer containing quantum dots and a p-type organic semiconductor, and a second light emitting layer containing an n-type organic semiconductor. This segmentation allows for separate optimization of hole transport and electron transport functions, improving exciton confinement and luminous efficiency while maintaining manageable device complexity
Solution Approach 2:
Each light emitting layer is given distinct local properties: the first layer is optimized for hole transport with p-type organic semiconductors having LUMO energy levels ≥ -3.0 eV, while the second layer is optimized for electron transport with n-type organic semiconductors having HOMO energy levels ≤ -7.0 eV. This local quality differentiation ensures proper charge carrier distribution and exciton confinement within the quantum dot layer
2Device complexity
If the energy level alignment at interfaces is not optimized, then the device structure is simple, but hole flow is inconsistent leading to exciton trapping
Solution Approach 1:
The energy level parameters of the organic semiconductors are specifically optimized: p-type organic semiconductors in the first light emitting layer have LUMO energy levels ≥ -3.0 eV to facilitate hole transport, while n-type organic semiconductors in the second light emitting layer have HOMO energy levels ≤ -7.0 eV to facilitate electron transport. These parameter changes ensure consistent hole flow and prevent exciton trapping at interfaces
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 luminous efficiency and extends the lifespan of the electroluminescent device by ensuring consistent electron-hole recombination within the light emitting layer, improving both efficiency and stability.
Implementation Method 1
Quantum dots are materials that exhibit quantum confinement effects as nanocrystals of semiconductor materials having diameters of several nanometers to several tens of nanometers. Quantum dots emit light when the excited electrons transition from a conduction band to a valence band, and the wavelength of the emitted light depends upon a particle size of the quantum dots
Implementation Method 2
Quantum dot electroluminescent devices
Implementation Method 3
In order to improve the quantum efficiency, excitons may be confined to the light emitting layer, but when the excitons are not so confined due to a variety of factors this can lead to a problem such as exciton quenching and consequent reduction in the luminous efficiency of the light emitting layer
Data Source
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AI summary
An electroluminescent device and a display device including the same are disclosed, wherein the electroluminescent device includes a first electrode; a hole transport layer disposed on the first electrode; a light emitting layer including a first light emitting layer disposed on the hole transport layer, the first emitting layer including a first quantum dot, and a second light emitting layer including a second quantum dot and an n-type organic semiconductor, the second light emitting layer disposed on the first light emitting layer; an electron transport layer disposed on the second light emitting layer; and a second electrode disposed on the electron transport layer.