White OLED Stacks with Balanced Charge Injection
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Solution Overview
Problem
Current white organic light emitting devices suffer from insufficient efficiency and variation in color characteristics during long-time driving, failing to achieve a broad color gamut and increased lifespan due to inefficient stack structures.
Innovation Solution
A white organic light emitting device with multiple stacks, including a green and red emission layer in contact, utilizing a single electron transport host and dopant with specific energy levels to equalize hole and electron injection, and a blue emission layer, achieving balanced energy band gaps for improved efficiency and lifespan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional stack structures with multiple emission layers are used, then the device can emit multiple colors of light, but the efficiency varies for each color and color characteristics vary during long-time driving
Solution Approach 1:
The patent adjusts the HOMO and LUMO energy levels of host and dopant materials in each emission layer to achieve balanced charge injection. Specifically, the energy level differences between adjacent emission layers are controlled to ensure equal hole and electron injection efficiency, which stabilizes color characteristics during long-time driving while maintaining manufacturing simplicity
Solution Approach 2:
The patent applies different host and dopant materials with specific energy levels to different emission layers (green, red, blue) to optimize local charge injection characteristics. Each emission layer is designed with tailored energy levels to achieve balanced charge transport, resulting in stable color characteristics across all layers during operation
2Illumination intensity
If emission layers with different photoluminescence peaks are stacked to achieve white light emission, then the color gamut can be expanded, but the efficiency and lifespan are insufficient
Solution Approach 1:
The patent optimizes the energy level parameters (HOMO and LUMO) of host and dopant materials in each emission layer to achieve balanced charge injection. This parameter optimization ensures efficient recombination and light emission across all color layers, expanding the color gamut while significantly improving device lifespan through enhanced operational stability
Solution Approach 2:
The patent uses composite material systems where each emission layer combines specific host materials (e.g., mCP, TCTA, BCP) with dopant materials having complementary energy levels. This composite approach enables simultaneous achievement of broad color gamut through multiple photoluminescence peaks and extended lifespan through balanced charge transport across all layers
3Power
If multiple emission layers are stacked to achieve white light emission, then multiple colors can be emitted, but hole injection and electron injection are not equalized leading to reduced efficiency
Solution Approach 1:
The patent systematically adjusts the HOMO and LUMO energy level parameters of host and dopant materials to achieve equal hole and electron injection. By controlling the energy level differences between adjacent emission layers, the patent optimizes charge transport efficiency across the stack, maximizing light emission efficiency while managing the complexity through methodical parameter optimization
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 solution results in a broader color gamut and increased lifespan by ensuring efficient electron and hole injection, preventing accumulation and enhancing luminous efficacy through balanced charge injection and transport.
Implementation Method 1
the emission layers including emissive materials having different photoluminescence (PL) peaks for each wavelength, white light being generated via the combination of light emitted from the multiple layers
Data Source
AI summary
A white organic light emitting device, which is increased in color gamut and lifespan, is discussed and an organic light emitting display device using the same and in a stack having different emission layers disposed in contact with each other, particular properties of a host and a dopant in a major emission layer are used.