Organic EL Device Intermediate Layer Triplet Energy Transfer
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Solution Overview
Problem
Organic electroluminescent devices with phosphorescent and fluorescent layers stacked in contact suffer from insufficient luminous efficiency due to triplet energy transfer from the phosphorescent layer to the fluorescent layer, leading to increased drive voltage and reduced efficiency in light emission.
Innovation Solution
Incorporating an intermediate layer with a hole transport layer and an electron transport layer, where the electron transport layer is on the anode side and the hole transport layer is on the cathode side, between the phosphorescent and fluorescent layers, with specific thicknesses to prevent triplet energy transfer and optimize light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the phosphorescent layer and fluorescent layer are stacked in contact with each other, then the device structure is simple, but triplet energy transfer occurs from the phosphorescent layer to the fluorescent layer resulting in insufficient luminous efficiency
Solution Approach 1:
An intermediate layer is inserted between the phosphorescent layer and fluorescent layer to prevent direct contact. This intermediate layer acts as a mediator that blocks triplet energy transfer from the phosphorescent layer to the fluorescent layer, thereby maintaining high luminous efficiency while preserving the stacked layer structure.
Solution Approach 2:
The intermediate layer is divided into two functional sub-layers: an electron transport layer adjacent to the phosphorescent layer and a hole transport layer adjacent to the fluorescent layer. This segmentation allows each sub-layer to perform its specific function (electron transport or hole transport) while collectively preventing triplet energy transfer.
2Loss of energy
If an intermediate layer is provided between the phosphorescent layer and fluorescent layer to prevent triplet energy transfer, then luminous efficiency is improved, but drive voltage increases
Solution Approach 1:
Different regions of the intermediate layer are assigned different material properties: the electron transport layer uses materials with appropriate electron mobility and LUMO levels, while the hole transport layer uses materials with appropriate hole mobility and HOMO levels. This local optimization allows efficient charge transport at low voltages while maintaining the energy blocking function.
Solution Approach 2:
The thickness of each layer in the intermediate structure is optimized to specific ranges (electron transport layer: 5-20 nm, hole transport layer: 5-20 nm) to balance the competing requirements of preventing triplet energy transfer (requiring sufficient thickness) and maintaining low drive voltage (requiring minimal thickness).
3Loss of energy
If the electron transport layer and hole transport layer are both provided with sufficient thickness to prevent energy transfer, then triplet energy blocking is effective, but device complexity and manufacturing difficulty increase
Solution Approach 1:
Rather than making each layer excessively thick to ensure energy blocking, the patent uses partially sufficient thickness (5-20 nm for each layer) combined with the synergistic effect of having both electron and hole transport layers. This partial action approach achieves effective energy blocking while keeping manufacturing complexity manageable.
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 enables efficient emission of phosphorescent and fluorescent light at low drive voltage, improving luminous efficiency and preventing an increase in drive voltage, allowing for balanced emission of red, green, and blue lights to produce white light effectively.
Implementation Method 1
a phosphorescent layer and a fluorescent layer that are provided between the anode and the cathode and emit phosphorescent light and fluorescent light, respectively, upon energization of the electrodes
Implementation Method 2
Organic electroluminescent devices (organic EL devices) are light-emitting devices having at least one luminescent organic layer interposed between an anode and a cathode. In this type of light-emitting device, electrons and holes are injected from the cathode side and the anode side, respectively, into the luminescent layer upon application of an electric field between the cathode and the anode. The electrons and the holes recombine within the luminescent layer to form excitons. The excitons then return to the ground state, releasing energy in the form of light.
Implementation Method 3
a phosphorescent layer and a fluorescent layer that are provided between the anode and the cathode and emit phosphorescent light and fluorescent light, respectively, upon energization of the electrodes
Implementation Method 4
Organic electroluminescent devices (organic EL devices) are light-emitting devices having at least one luminescent organic layer interposed between an anode and a cathode. In this type of light-emitting device, electrons and holes are injected from the cathode side and the anode side, respectively, into the luminescent layer upon application of an electric field between the cathode and the anode. The electrons and the holes recombine within the luminescent layer to form excitons. The excitons then return to the ground state, releasing energy in the form of light.
Implementation Method 5
In the case where such a light-emitting device is configured such that the phosphorescent layer and the fluorescent layer are stacked in contact with each other, the triplet energy of the phosphorescent layer is transferred toward the fluorescent layer and is thereafter deactivated without contributing to light emission
Data Source
AI summary
A light-emitting device includes an anode, a cathode, a first phosphorescent layer and a fluorescent layer that are provided between the anode and the cathode and emit phosphorescent light and fluorescent light, respectively, upon energization of the anode and the cathode, and an intermediate layer provided between the first phosphorescent layer and the fluorescent layer, the intermediate layer including a hole transport layer and an electron transport layer that are in contact with each other, the electron transport layer being located on the anode side, the hole transport layer being located on the cathode side.