OLED Buffer Layer LUMO Level Control for Color Uniformity
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Solution Overview
Problem
Organic light emitting devices face challenges in maintaining efficiency and lifespan in high gray regions while reducing efficiency in low gray regions, leading to color non-uniformity, particularly in green organic light emitting elements.
Innovation Solution
Incorporating a buffer layer with a first material having a lowest unoccupied molecular orbital (LUMO) level higher than the electron transport layer, and optionally including a second material with faster electron mobility, to control electron injection and emission efficiency across different gray regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If emission efficiency is improved in high gray regions, then lifespan and efficiency are maintained, but color non-uniformity occurs in low gray regions
Solution Approach 1:
The buffer layer is designed with specific local properties (LUMO level higher than electron transport layer by 0.3 eV or greater) to selectively control electron injection in different gray regions. This local quality difference allows the buffer layer to reduce efficiency specifically in low gray regions while maintaining high efficiency in high gray regions, resolving the color uniformity issue without sacrificing lifespan.
Solution Approach 2:
The invention changes the energy level parameter of the buffer layer (LUMO level) to be higher than that of the electron transport layer by at least 0.3 eV. This parameter change creates an energy barrier that selectively modulates electron injection, reducing efficiency in low gray regions to prevent color non-uniformity while preserving efficiency and lifespan in high gray regions.
2Use of energy by moving object
If current efficiency is improved in low brightness region, then brightness control is enhanced, but brightness deviation occurs due to TFT driving current deviation
Solution Approach 1:
The buffer layer acts as an intermediary between the emission layer and the electron transport layer. It mediates electron injection by providing an energy barrier (higher LUMO level) that reduces electron injection efficiency in low brightness regions. This intermediary function compensates for TFT driving current deviations, preventing brightness deviation and improving overall brightness uniformity.
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 solution effectively reduces efficiency in low gray regions to prevent color non-uniformity while maintaining high efficiency and lifespan in high gray regions, as demonstrated by improved emission efficiency and lifespan graphs compared to comparative examples.
Implementation Method 1
the buffer layer includes a first material having a lowest unoccupied molecular orbital (LUMO) level that is higher than that of the electron transport layer
Data Source
AI summary
An organic light emitting element according to an example embodiment of the present disclosure includes: a first electrode and a second electrode facing each other; an emission layer between the first electrode and the second electrode; an electron transport layer between the emission layer and the second electrode; and a buffer layer between the emission layer and the electron transport layer, wherein the buffer layer includes a first material having a higher LUMO level than that of the electron transport layer.