Indolocarbazole Host for Organic EL Charge Balance
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Solution Overview
Problem
Existing organic electroluminescent devices face challenges in achieving high luminous efficiency and driving stability due to imbalances in charge injection and transport, particularly when using host materials like 4,4'-bis(9-carbazolyl)biphenyl (CBP) which facilitates hole delivery over electron delivery, leading to reduced efficiency and stability.
Innovation Solution
Incorporating an indolocarbazole compound with a specific structure, featuring a nitrogen-containing six-membered ring and a fused heterocyclic substituent, in at least one organic layer of the device, such as a phosphorescent light-emitting layer, hole-transporting layer, electron-transporting layer, or hole-blocking layer, to enhance charge balance and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If CBP is used as host material to facilitate hole delivery, then hole transport efficiency is improved, but electron transport efficiency deteriorates leading to charge imbalance
Solution Approach 1:
The patent applies local quality by using different host materials in different regions of the device. Specifically, it uses a first host material (CBP) in the hole-transporting layer that excels at hole transport, and a second host material (indolocarbazole compound) in the electron-transporting layer that provides balanced electron and hole transport. This regional differentiation resolves the charge balance issue while maintaining high hole transport efficiency where needed.
Solution Approach 2:
The patent employs composite materials by combining CBP with an indolocarbazole compound having a nitrogen-containing six-membered ring in the electron-transporting layer. This composite approach leverages the strengths of both materials: CBP's hole transport capability and the indolocarbazole compound's electron transport and charge balancing properties, achieving overall device performance optimization.
2Use of energy by moving object
If phosphorescent light emission is used to improve luminous efficiency, then theoretical luminous efficiency increases, but achieving high luminance and stability remains difficult
Solution Approach 1:
The patent applies parameter changes by carefully selecting and optimizing the molecular structure parameters of the indolocarbazole compound, specifically incorporating a nitrogen-containing six-membered ring. This structural modification changes the electronic properties (HOMO/LUMO levels, triplet energy) to achieve both high phosphorescent luminous efficiency and driving stability, resolving the contradiction between theoretical efficiency and practical stability.
3Reliability
If indolocarbazole compound with nitrogen-containing six-membered ring is used in electron-transporting layer, then charge balance is improved, but device complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the device into distinct functional layers with specific materials optimized for each layer's purpose. The indolocarbazole compound is specifically placed in the electron-transporting layer where it is most needed for charge balance, rather than uniformly throughout the device. This targeted segmentation achieves charge balance improvement while minimizing overall device complexity.
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 indolocarbazole compound improves luminous efficiency and driving stability by optimizing charge injection and transport, resulting in enhanced light-emitting characteristics and a longer driving lifetime, making the organic electroluminescent device more suitable for flat panel displays and other applications.
Implementation Method 1
the optimization of the kind of electrodes has been attempted for the purpose of improving the efficiency of injection of carriers from the electrodes
Implementation Method 2
electrons are injected from a cathode and holes are injected from an anode, and each electron and each hole recombine in the light-emitting layer to emit light
Implementation Method 3
by using phosphorescent light emission, that is, by using light emission from a triplet excited state, luminous efficiency is expected to be improved by about three times to four times
Data Source
Figure 1~2
Figure 3
AI summary
Provided is an organic electroluminescent device (EL device) using an indolocarbazole compound. The organic EL device is obtained by laminating an anode, a plurality of organic layers including a phosphorescent light-emitting layer, and a cathode on a substrate, and the phosphorescent light-emitting layer, a hole-transporting layer, an electron-transporting layer, a hole-blocking layer, or an electron-blocking layer contains an indolocarbazole compound represented by the general formula (1). In the general formula (1), a ring I and a ring II represent rings represented by the formula (1a) and the formula (1b) to be fused to adjacent rings, As each represent C-R or N and at least one of As represents N, Ls each represent a substituted or unsubstituted aromatic hydrocarbon group, or a substituted or unsubstituted aromatic heterocyclic group, and at least one of Ls represents a two- to four-ring fused heterocyclic group, Rs each represent an aliphatic hydrocarbon group, an aromatic hydrocarbon group, or an aromatic heterocyclic group, ps each represent an integer of from 0 to 4, q represents an integer of from 0 to 2, r represents an integer of from 1 to 4, X1 to X4 each represent an aromatic hydrocarbon group or an aromatic heterocyclic group, and l, m, and n each represent an integer of from 0 to 5.