OLED Multi-Layered Hole Transporting Layer for Charge Balance
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Solution Overview
Problem
Conventional organic light-emitting diodes (OLEDs) face issues with low efficiency and short lifespan due to excessive charge injection and imbalance, despite using high hole mobility materials in the hole transporting layer, which leads to reduced luminescence efficiency and shorter device lifetime.
Innovation Solution
The implementation of a multi-layered hole transporting layer structure incorporating two different hole transporting compounds with varying hole injection and charge generation characteristics, along with specific charge generation materials and a buffer layer, to enhance charge balance and stability, thereby improving the OLED's efficiency and lifespan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a hole transport material having high hole mobility is used in a hole transporting layer, then the driving voltage is substantially decreased, but charges are excessively injected resulting in low efficiency and short lifespan
Solution Approach 1:
The hole transporting layer is divided into multiple sub-layers (first hole transporting layer, second hole transporting layer, third hole transporting layer) with different hole mobility characteristics. This segmentation allows each layer to perform specialized functions: the first layer provides high hole mobility for efficient transport, while the second and third layers provide lower hole mobility to prevent excessive charge injection and exciton quenching, thereby resolving the contradiction between low driving voltage and device reliability
Solution Approach 2:
Different regions of the hole transporting layer are assigned different material properties with specific hole mobility values. The first hole transporting layer uses materials with high hole mobility (μh ≥ 10^-5 cm²/Vs) for efficient charge transport, while the second and third layers use materials with progressively lower hole mobility (10^-6 ≤ μh < 10^-5 and 10^-7 ≤ μh < 10^-6 cm²/Vs respectively) to control charge injection at different interfaces, achieving local optimization of charge management
2Productivity
If high hole mobility materials are used to improve charge transport, then hole transport function is enhanced, but charge balance deteriorates due to excessive charge injection
Solution Approach 1:
The hole transporting layer is segmented into three distinct layers with progressively decreasing hole mobility from the anode interface toward the emission layer. This segmentation creates a gradient structure that facilitates efficient hole transport near the anode while progressively reducing hole density toward the emission layer, preventing charge accumulation and maintaining charge balance
Solution Approach 2:
The hole mobility parameter is systematically varied across different layers of the hole transporting layer. By selecting materials with specific hole mobility ranges for each layer, the patent creates an optimized charge transport pathway that maintains high productivity while preventing excessive charge injection that would disrupt charge balance
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 results in improved charge balance, increased luminescence efficiency, and extended device lifetime by controlling hole mobility and reducing exciton quenching, while maintaining low driving voltage.
Implementation Method 1
The holes and electrons, which are carriers, are recombined in the emission layer to generate excitons, and then the excitons change from an excited state to a ground state, thereby generating light
Data Source
AI summary
An organic light-emitting diode including: a first mixed layer between an emission layer and a first electrode and including first and second compounds; a second mixed layer between the emission layer and the first mixed layer and including third and fourth compounds; a first charge generation layer between the first mixed layer and the first electrode and including the first and second compounds and a first charge generation material; a second charge generation layer between the first mixed layer and the second mixed layer and including the third and fourth compounds and a second charge generation material; and a buffer layer between the emission layer and the second mixed layer, the first and the third compounds are each independently a compound represented by Formula 1 below, and the second compound and fourth compounds are each independently a compound represented by Formula 2 below: