Dual Emission Layer OLED Device Suppressing Roll-Off
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Solution Overview
Problem
Existing light-emitting devices face efficiency issues due to roll-off phenomena at high voltages, where surplus charges are quenched, leading to decreased luminescence efficiency, particularly in emission layers with single host and dopant configurations.
Innovation Solution
A light-emitting device with a dual emission layer structure, where the first emission layer includes a hole-transporting host (HTH1) and electron-transporting host (ETH1) with specific mobility characteristics, and the second emission layer includes HTH2 and ETH2, both potentially containing deuterium, to control hole and electron mobility, reducing exciton-polaron and polaron-polaron quenching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single host and dopant configuration is used in the emission layer, then the device structure is simple, but roll-off phenomena occur at high voltages causing decreased luminescence efficiency
Solution Approach 1:
The emission layer is divided into two distinct emission layers (first emission layer and second emission layer), each with different host materials and dopants. This segmentation allows independent optimization of electron transport and hole transport characteristics, preventing charge accumulation and roll-off phenomena that occur in single-layer structures.
Solution Approach 2:
The patent uses composite material structures where the first emission layer contains a first host and first dopant, while the second emission layer contains a second host and second dopant. This composite approach combines materials with complementary properties to achieve balanced charge transport and maintain high luminescence efficiency across different voltage conditions.
2Illumination intensity
If high voltage is applied to increase luminance, then brightness increases, but surplus charges are quenched leading to decreased efficiency
Solution Approach 1:
Different regions of the emission structure are assigned different material properties: the first emission layer is optimized for electron transport with appropriate electron mobility, while the second emission layer is optimized for hole transport. This local quality differentiation ensures that charges are efficiently transported and recombined at appropriate locations, preventing quenching even at high voltages.
Solution Approach 2:
The patent carefully controls and adjusts the mobility parameters of the host materials in each emission layer. By optimizing the mobility of electrons and holes in their respective layers, the device maintains efficient charge transport and recombination across a wide voltage range, preventing the quenching effect that reduces efficiency at high voltages.
3Speed
If electron mobility in ETH1 is increased to improve electron transport, then electron transport efficiency improves, but device complexity increases due to dual emission layer structure
Solution Approach 1:
The device segments the emission function into two separate layers, allowing each layer to be independently optimized for its primary charge carrier type. This segmentation enables high electron mobility in the first emission layer without compromising the overall device structure, as each layer's complexity is managed independently.
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 dual emission layer structure enhances efficiency and lifespan by suppressing roll-off phenomena, maintaining high luminescence efficiency across varying voltages and improving overall device performance.
Implementation Method 1
the first emission layer includes a first hole-transporting host (HTH1), a first electron-transporting host (ETH1), and a first phosphorescent dopant (G1), the second emission layer includes a second hole-transporting host (HTH2), a second electron-transporting host (ETH2), and a second phosphorescent dopant (G2)
Data Source
AI summary
A light-emitting device includes a first emission layer and a second emission layer, wherein the first emission layer includes a first hole-transporting host (HTH1), a first electron-transporting host (ETH1), and a first phosphorescent dopant (G1), and the second emission layer includes a second hole-transporting host (HTH2), a second electron-transporting host (ETH2), and a second phosphorescent dopant (G2). The electron mobility of the ETH1 is faster than the electron mobility of the ETH2, the hole mobility of the HTH2 is faster than the hole mobility of the HTH1, and the HTH1 and/or HTH2 includes deuterium.