Organic EL Device Charge Blocking Layer Triplet Energy Management
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current organic EL devices fail to achieve high luminous efficiency for mixed-color emission due to the deactivation of excited triplet states in blue emitting layers, leading to reduced blue emission intensity and inefficient energy utilization.
Innovation Solution
An organic EL device structure is implemented with a phosphorescent-emitting layer, a charge blocking layer, and a fluorescent-emitting layer, where the triplet energy gaps and affinity levels of the materials satisfy specific formulas to efficiently transfer excited triplet energy from the fluorescent host to the phosphorescent dopant, enabling both fluorescence and phosphorescence contributions to emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If phosphorescent materials are used to enhance luminous efficiency by utilizing excited triplet states, then luminous efficiency is improved, but blue emission intensity is reduced due to small energy gap causing triplet deactivation
Solution Approach 1:
The patent introduces a charge blocking layer as an intermediary between the blue fluorescent-emitting layer and the red/green phosphorescent-emitting layers. This layer has a triplet energy gap specifically designed to block triplet energy transfer to the phosphorescent layers while allowing charge separation. This mediator resolves the contradiction by preventing the deactivation pathway that would otherwise reduce blue emission intensity, while still allowing the phosphorescent layers to utilize triplet states from their own excitons for enhanced overall luminous efficiency
Solution Approach 2:
The patent applies different material properties to different layers: the blue emitting layer uses fluorescent materials with large triplet energy gaps to maintain blue emission intensity, while the red/green emitting layers use phosphorescent materials to utilize triplet states for enhanced efficiency. The charge blocking layer has intermediate properties that locally control energy and charge transport. This local differentiation allows each layer to optimize its emission characteristics without compromising the other
2Use of energy by moving object
If excited triplet energy is diffused from blue emitting layer to red and green emitting layers, then luminous efficiency is enhanced, but blue emission intensity is reduced
Solution Approach 1:
The charge blocking layer acts as an energy transport intermediary that is selectively permeable. Its triplet energy gap is engineered to be larger than that of the phosphorescent materials but smaller than or equal to that of the fluorescent host. This allows the layer to accept triplet energy from the blue fluorescent layer and transfer it to the red/green phosphorescent layers, while its charge-blocking function prevents direct charge injection that would otherwise reduce blue emission. This mediator enables controlled energy diffusion that enhances overall efficiency without excessive blue energy loss
Solution Approach 2:
The patent carefully controls the triplet energy gap parameter of the charge blocking layer to satisfy specific inequalities relative to the fluorescent host and phosphorescent dopant. By adjusting this parameter, the system optimizes the balance between allowing triplet energy diffusion to enhance efficiency and maintaining sufficient blue emission intensity. This parameter optimization resolves the contradiction between energy utilization and energy loss
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 significantly enhances luminous efficiency by effectively utilizing excited triplet energy for phosphorescence, resulting in improved blue emission intensity and overall mixed-color emission performance.
Implementation Method 1
a phosphorescent-emitting layer, a charge blocking layer, and a fluorescent-emitting layer, where the triplet energy gaps and affinity levels of the materials satisfy specific formulas to efficiently transfer excited triplet energy from the fluorescent host to the phosphorescent dopant, enabling both fluorescence and phosphorescence contributions to emission
Implementation Method 2
Excited state of organic compounds encompasses excited singlet state and excited triplet state. Emission obtained from excited singlet state is called fluorescence
Implementation Method 3
the charge blocking layer blocking the electrons injected into the fluorescent-emitting layer from being injected toward the charge blocking layer from the fluorescent-emitting layer, the charge blocking layer also injecting the holes into the fluorescent-emitting layer from the phosphorescent-emitting layer
Data Source
AI summary
A phosphorescent-emitting layer contains a phosphorescent host and a phosphorescent dopant for providing phosphorescence, and a fluorescent-emitting layer contains a fluorescent host and a fluorescent dopant for providing fluorescence. A charge blocking layer blocks electrons injected into the fluorescent host of the fluorescent-emitting layer from being injected toward the charge blocking layer from the fluorescent-emitting layer, and also injects holes into the fluorescent-emitting layer from the phosphorescent-emitting layer. A triplet energy gap EgPD of the phosphorescent dopant of the phosphorescent-emitting layer, a triplet energy gap EgEB of the charge blocking layer and a triplet energy gap EgFH of the fluorescent host of the fluorescent-emitting layer satisfy the following formula (1).EgPD<EgEB≦EgFH (1)