Organic Light-Emitting Element Carrier Control Layer
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Solution Overview
Problem
Current current-excitation light-emitting elements with organic compounds face challenges in achieving long lifetime due to issues with carrier balance and luminance decay, particularly because existing hole blocking layers are not durable.
Innovation Solution
Incorporating a layer for controlling carrier movement between the light-emitting layer and electrodes, composed of a first organic compound with electron or hole transporting properties and a second organic compound with electron or hole trapping properties, where the second compound has a molecular orbital level significantly different from the first, to manage carrier balance and recombination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a hole blocking layer is provided to improve luminous efficiency, then luminous efficiency is improved, but the layer is not durable and the light-emitting element has a short lifetime
Solution Approach 1:
The patent uses a composite material consisting of a host compound and a guest compound with electron trapping properties. The host compound provides the basic electron transporting function, while the guest compound (e.g., coumarin derivatives, quinacridone derivatives, or benzothiazole derivatives) introduces electron trapping capability to balance carrier distribution. This composite approach maintains durability while improving luminous efficiency by preventing excessive electron accumulation that degrades the hole blocking layer.
Solution Approach 2:
The patent changes the molecular orbital parameters of the layer materials by selecting compounds with specific LUMO levels. The guest compound is chosen to have a LUMO level that is 0.3 eV or more lower than the host compound, creating an energy level difference that enables effective electron trapping. This parameter change allows the layer to simultaneously block holes and trap electrons, improving both efficiency and lifetime.
2Device complexity
If carrier balance is not controlled, then the structure is simpler, but carrier balance changes over time causing luminance decay
Solution Approach 1:
The patent introduces an intermediary layer between the light-emitting layer and the hole blocking layer. This intermediary layer contains the host-guest composite material that actively mediates carrier balance by trapping excess electrons and preventing them from reaching the hole blocking layer. This intermediary function maintains luminance stability without requiring complex multi-layer structures, as the single composite layer performs multiple functions.
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 approach suppresses changes in carrier balance over time, leading to a longer lifetime for the light-emitting element with improved luminous efficiency and reduced power consumption, while preventing luminance decay.
Implementation Method 1
the first organic compound is an organic compound having an electron transporting property
Implementation Method 2
the second organic compound is an organic compound having an electron trapping property
Implementation Method 3
By applying a voltage to such an element, light emission can be obtained from the light-emissive compound
Data Source
AI summary
The light-emitting element includes: a light-emitting layer and a layer for controlling the movement of carriers between a first electrode and a second electrode. The layer for controlling the movement of carriers contains a first organic compound and a second organic compound, and is provided between the light-emitting layer and the second electrode. The first organic compound has an electron transporting property, and the second organic compound has an electron trapping property. The weight percent of the first organic compound is higher than that of the second organic compound. The light-emitting layer emits light when a voltage is applied such that the potential of the first electrode is higher than that of the second electrode.