Organic EL Device Mixed Host Material Triplet Energy Confinement
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Solution Overview
Problem
Current organic electroluminescent elements face challenges in achieving high luminous efficiency and driving stability while being capable of operation at low voltages, with existing host materials failing to provide efficient light emission and long lifetimes.
Innovation Solution
The use of a mixed host structure in the light-emitting layer, comprising specific compounds represented by general formulae (1) and (2), along with a light-emitting dopant, such as an organometallic complex, to confine the lowest excited triplet energy and prevent energy outflow, thereby enhancing efficiency and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional host materials (carbazole-based, oxazole-based, triazole-based compounds) are used in the light-emitting layer, then the device structure can be maintained, but high luminous efficiency and long lifetime cannot be achieved simultaneously
Solution Approach 1:
The patent uses a composite host material system consisting of an indolocarbazole compound (Formula 1) combined with a carbazole compound (Formula 2) in specific weight ratios (95:5 to 5:95). This composite structure leverages the complementary properties of both materials: the indolocarbazole compound provides high triplet energy and stability, while the carbazole compound enhances hole transport and luminescence efficiency, achieving both high luminous efficiency and long lifetime that neither material can achieve alone.
Solution Approach 2:
The patent optimizes the weight ratio parameters of the mixed host materials to achieve maximum performance. By adjusting the proportion of indolocarbazole compound and carbazole compound within the 95:5 to 5:95 range, the device can balance between stability (from indolocarbazole) and luminescence efficiency (from carbazole), resolving the contradiction between lifetime and luminous efficiency through parameter optimization.
2Productivity
If phosphorescent light-emitting materials are used to improve luminous efficiency, then efficiency can be increased by 3-4 times, but previously available phosphorescent dopants (coumarin derivative, benzophenone derivative, europium complex) provide extremely low luminance
Solution Approach 1:
The patent introduces a specifically designed indolocarbazole compound as a host material that acts as an intermediary between the phosphorescent dopant and the electrode. This host material has optimized triplet energy levels that effectively confine the excited triplet state of the phosphorescent dopant, preventing energy loss while enabling efficient energy transfer. This intermediary host material resolves the contradiction by providing both the efficiency enhancement of phosphorescence and the high luminance needed for practical applications.
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 high luminous efficiency and extended lifetime of the organic electroluminescent element, allowing it to be driven at low voltages with improved performance in flat panel displays and light sources.
Implementation Method 1
to confine the lowest excited triplet energy and prevent energy outflow, thereby enhancing efficiency and stability
Implementation Method 2
when an electric field is applied between both the electrodes, 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 as energy
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
AI summary
Provided is a practically useful organic EL element having high efficiency and high driving stability while being capable of being driven at a low voltage. The organic EL element has a light-emitting layer and any other organic layer between an anode and a cathode opposite to each other. The light-emitting layer contains at least two host materials and at least one light-emitting dopant. At least one of the host materials is a host material selected from compounds each having one or two indolocarbazole skeletons, and at least one of the other host materials is a host material selected from carbazole compounds each substituted with a dibenzofuran or a dibenzothiophene.