OLED Electron Control Layer for Luminous Efficiency and Black State Leakage
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Solution Overview
Problem
Organic light-emitting devices (OLEDs) using phosphorescent materials face challenges in achieving satisfactory luminous efficiency, particularly at low luminance regions, leading to unwanted emission of green or red light during black states due to current leakage.
Innovation Solution
Incorporating an electron control layer with specific energy level characteristics and compositions between the phosphorescent emission layer and the electron transport layer, along with an electron blocking layer, to balance electron and hole injection and transportation, thereby suppressing unwanted light emission at low luminance regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a phosphorescent material is used in the emission layer, then luminous efficiency is improved at high luminance regions, but unwanted light emission occurs at low luminance regions due to current leakage
Solution Approach 1:
An electron control layer is introduced as an intermediary between the phosphorescent emission layer and the electron transport layer. This layer mediates electron injection by providing energy levels that facilitate electron injection at high luminance while suppressing it at low luminance, thereby preventing current leakage and unwanted light emission in the black state
Solution Approach 2:
The electron control layer utilizes specific energy level parameters (HOMO and LUMO levels) to achieve different electron injection characteristics. By selecting materials with appropriate energy levels (|EH H - EH C | ≤ 0.3 eV and |EL H - EL C | ≤ 0.5 eV), the system achieves high electron injection efficiency at high luminance while maintaining low injection at low luminance, resolving the contradiction between luminous efficiency and current leakage
2Productivity
If electron injection is enhanced to improve luminous efficiency, then high luminance performance is improved, but current leakage increases at low luminance regions
Solution Approach 1:
The electron control layer provides dynamic electron injection control based on operating conditions. At high luminance, the energy level alignment facilitates strong electron injection for high efficiency. At low luminance, the same structure naturally suppresses electron injection, preventing current leakage. This dynamic behavior resolves the contradiction between productivity 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
The solution significantly improves luminous efficiency at high luminance regions while reducing efficiency at low luminance regions, effectively preventing the emission of red and green light during black states, enhancing overall OLED performance.
Implementation Method 1
When a voltage is applied between the anode and the cathode, holes injected from the anode pass the hole transport layer and migrate toward the emission layer, and electrons injected from the cathode pass the electron transport layer and migrate toward the emission layer. Carriers such as the holes and electrons are recombined in the emission layer to generate excitons, and then the excitons change from an excited state to a ground state, thereby generating light.
Implementation Method 2
an electron control layer disposed between the phosphorescent emission layer and the electron transport layer
Data Source
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AI summary
An organic light-emitting device including a first electrode, a second electrode opposite to the first electrode, a phosphorescent layer disposed between the first electrode and the second electrode, an electron transport layer disposed between the phosphorescent emission layer and the second electrode, and an electron control layer disposed between the phosphorescent emission layer and the electron transport layer. An organic light-emitting display apparatus including the OLED is also disclosed.