Trapping Layer Energy Alignment for OLED Lifespan and Voltage
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Solution Overview
Problem
Organic light emitting devices face challenges in increasing lifespan and reducing driving voltage due to electron leakage from the electron blocking layer, which causes deterioration of the hole transport layer and higher voltage requirements.
Innovation Solution
Incorporating a trapping layer between the hole transport layer and the electron blocking layer with a LUMO energy level similar to or equal to the HOMO energy level of the electron blocking layer, capturing escaped electrons and allowing smooth hole transport, thereby functioning as a charge generation layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an electron blocking layer is provided between the hole transport layer and the organic light emitting layer, then electron leakage is prevented and emission efficiency is improved, but electrons escape to the hole transport layer causing deterioration and higher driving voltage
Solution Approach 1:
A trapping layer with LUMO level of -6.0 eV to -4.5 eV is introduced between the hole transport layer and electron blocking layer to act as an intermediary that captures escaped electrons and prevents them from reaching the hole transport layer, thereby protecting the hole transport layer from deterioration while maintaining emission efficiency
Solution Approach 2:
The electron blocking function is segmented into two parts: the electron blocking layer (with HOMO level of -5.5 eV to -5.0 eV) that blocks electrons from the organic light emitting layer, and the trapping layer (with LUMO level of -6.0 eV to -4.5 eV) that captures escaped electrons, dividing the protective function across two specialized layers
2Reliability
If an electron blocking layer with broad bandgap is used to block electrons, then electron leakage is prevented, but known materials have narrow bandgap with high LUMO and HOMO levels causing insufficient hole injection and high driving voltage
Solution Approach 1:
The energy level parameters of the trapping layer are specifically designed with LUMO level of -6.0 eV to -4.5 eV to be lower than the HOMO level of the electron blocking layer, creating an energy gradient that enables the trapping layer to capture electrons while maintaining good hole injection capability and reducing driving voltage
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 trapping layer effectively increases the lifespan of the organic light emitting device by preventing electron leakage and reducing driving voltage, while maintaining high hole transport efficiency and emission efficiency.
Implementation Method 1
A LUMO energy level of the trapping layer differs from a HOMO energy level of the electron blocking layer within a range of 1 eV or is equal to the HOMO energy level
Implementation Method 2
Holes and electrons from the anode and cathode are injected into the organic light emitting layer and are combined with each other in the organic light emitting layer, thus generating excitons. When the generated excitons are changed from an excited state to a ground state, the organic light emitting diode emits light
Data Source
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AI summary
An organic light emitting device includes a trapping layer (140) between a hole transport layer (130) and an electron blocking layer (150) so as to increase a lifespan and decrease a driving voltage, and the trapping layer (140) has a LUMO energy relative to a HOMO energy of the electron blocking layer (150) contacting the trapping layer (140).