OLED Red Host Energy Alignment for Roll-Off Prevention
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Solution Overview
Problem
Conventional organic light emitting displays suffer from deterioration in contrast ratio and roll-off phenomenon at low gray scale due to high quantum efficiency of red light emitting layers and inefficient electron transport, leading to difficulties in forming a gamma curve and maintaining luminous efficacy across varying currents.
Innovation Solution
The organic light emitting display incorporates a red light emitting layer with a red host having a photo-luminescence peak maximum between 455 nm to 470 nm and an electron-transporting layer with a peak maximum between 435 nm to 495 nm, ensuring a gap of ±25 nm between the two, along with a multilayer structure for the second electrode and a front sealing layer to optimize electron transport and prevent roll-off.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a phosphorescent material is used for the red light emitting layer to achieve high quantum efficiency, then luminous efficacy is improved, but contrast ratio deteriorates due to light emission at zero gray scale
Solution Approach 1:
The patent changes the energy level parameters of the red host material by selecting materials with specific photo-luminescence peak maxima (455-470 nm) and controlling the energy gap with the electron-transporting layer. This parameter optimization allows the red light emitting layer to maintain high luminous efficacy while reducing light emission at zero gray scale, thereby improving contrast ratio.
2Use of energy by moving object
If the red light emitting layer is formed with phosphorescent material for high efficiency, then luminous efficacy is improved, but roll-off phenomenon occurs at low gray scale
Solution Approach 1:
The patent optimizes the energy level parameters by selecting red host materials with photo-luminescence peak maxima of 455-470 nm and controlling the energy gap with the electron-transporting layer to be within ±25 nm. This parameter control prevents excessive electron injection at low gray scales, maintaining stable efficiency across different gray scales and preventing roll-off phenomenon.
Solution Approach 2:
The red host material acts as an intermediary between the electron-transporting layer and the red dopant. By optimizing the energy gap between the red host and electron-transporting layer, the patent controls electron transport and energy transfer processes, preventing direct excessive electron injection into the red dopant that causes roll-off at low gray scales.
3Device complexity
If conventional materials are used in the electron-transporting layer, then device simplicity is maintained, but electron transport efficiency is insufficient leading to roll-off
Solution Approach 1:
The patent changes the material selection criteria for the electron-transporting layer by specifying photo-luminescence peak maximum ranges (435-495 nm) and energy gap requirements with the red host (±25 nm). This targeted material selection improves electron transport efficiency and prevents roll-off while maintaining reasonable device structure.
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 maintains constant luminous efficacy across low and high currents, prevents roll-off at low gray scale, and improves contrast ratio by ensuring efficient electron movement and energy alignment between the red host and electron-transporting layer.
Implementation Method 1
a gap between a photo-luminescence (PL) peak maximum of the red host of the red light emitting layer and a photo-luminescence (PL) peak maximum of the electron-transporting layer contacting the red light emitting layer is within ±25 nm
Implementation Method 2
Holes injected from the anode recombine with electrons injected from the cathode in a light emitting layer to form electron-hole pairs, i.e., excitons. When the excitons transition to a ground state, energy is released. Based on this energy, the organic light emitting display emits light.
Data Source
AI summary
An organic light emitting display includes first and second electrodes facing each other on a substrate, a red light emitting layer, a green light emitting layer and a blue light emitting layer formed between the first and second electrodes, a hole-transporting layer formed between the first electrode and each of the red light emitting layer, the green light emitting layer and the blue light emitting layer, and an electron-transporting layer formed between the second electrode and each of the red light emitting layer, the green light emitting layer and the blue light emitting layer, wherein a gap between a photo-luminescence (PL) peak maximum of the red host of the red light emitting layer and a photo-luminescence (PL) peak maximum of the electron-transporting layer contacting the red light emitting layer is within ±25 nm.