OLED Insertion Layer for Carrier Balance and Color Stability

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Solution Overview

Problem

Existing organic electroluminescent elements face issues with carrier imbalance, low light-emitting efficiency, and color change due to voltage variations, primarily caused by uneven electron and hole mobility and recombination zone shifts.

Innovation Solution

Incorporating an insertion layer within the light-emitting layer to adjust electron mobility, with specific molecular orbital levels and materials such as aromatic diamine compounds, triphenylamine compounds, and carbazole polymers, to balance electron and hole quantities and stabilize the recombination zone.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If the light-emitting layer uses a matrix material favoring electron transport, then electron mobility is improved, but carrier balance deteriorates and light-emitting efficiency decreases

Engineering Contradiction:

Improveelectron mobilityVSAvoidlight-emitting efficiency

Core Design Contradiction:

SpeedVSLoss of energy

Solution Approach 1:

An insertion layer is introduced as an intermediary between the electron transport layer and the light-emitting layer. This insertion layer acts as a mediator to regulate electron transport into the light-emitting layer, preventing excessive electron injection while maintaining good electron mobility in the overall device. The insertion layer has specific HOMO and LUMO levels that are intermediate between the electron transport layer and light-emitting layer, creating a energy barrier that controls carrier balance.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Productivity

If voltage is increased to improve carrier injection, then carrier injection efficiency is improved, but recombination zone position changes and color stability deteriorates

Engineering Contradiction:

Improvecarrier injection efficiencyVSAvoidcolor stability

Core Design Contradiction:

ProductivityVSStability of the object's composition

Solution Approach 1:

The insertion layer is designed with specific energy levels (HOMO and LUMO) that create a preliminary barrier against excessive electron injection at high voltages. By setting the LUMO level of the insertion layer higher than that of the light-emitting layer, the structure preemptively prevents electron overflow into the light-emitting layer even when high voltage is applied, thus maintaining stable recombination zone position and color output.

Inventive Principle:

Principle #9Preliminary anti-action

3Device complexity

If a single recombination zone is formed, then device structure is simplified, but carrier quantity mismatch increases and exciton quenching occurs

Engineering Contradiction:

Improvestructure complexityVSAvoidcarrier recombination efficiency

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The device is segmented into distinct functional layers with the insertion layer creating a separate electron blocking region. This segmentation allows the light-emitting layer to maintain a single recombination zone structure while the insertion layer prevents electron overflow, thereby maintaining high carrier recombination efficiency without increasing structural complexity significantly.

Inventive Principle:

Principle #1Segmentation

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 enhances light-emitting efficiency, stabilizes color output, and extends the lifespan of the electroluminescent element by ensuring balanced carrier recombination and reducing voltage-induced inefficiencies.

Implementation Method 1

At least one insertion layer for adjusting electron mobility is disposed within the light-emitting layer. The lowest unoccupied molecular orbital (LUMO) of the insertion layer is higher than the LUMO of the light-emitting layer, its highest occupied molecular orbital (HOMO) is equal to or lower than the HOMO of the light-emitting layer, and the electron mobility is lower than the hole mobility in the insertion layer.

Methodology Applied

Scientific EffectElectron mobility adjustment via molecular orbital levels:

Implementation Method 2

Organic light-emitting diode (OLED) display is also called organic electroluminescent display. When a voltage is applied to the light-emitting layer 103 via the anode layer 102 and the cathode layer 104, the hole mobility is higher than the electron mobility.

Methodology Applied

Scientific EffectElectroluminescence: Electroluminescence

Data Source

PatentUS9209416B2Electroluminescent element, display device and method for preparing electroluminescent element

Publication Date: 2015.12.08 BOE TECHNOLOGY GROUP CO LTD

AI summary

Disclosed are an electroluminescent element, a display device and a method for preparing the electroluminescent element. The electroluminescent element comprises a substrate (101) and an anode layer (102), a light-emitting layer (103) and a cathode layer (104) that are disposed in sequence on the substrate (101). At least one insertion layer (105) for adjusting electron mobility is disposed within the light-emitting layer (103). By disposing an insertion layer (105) in the light-emitting layer (103), the effect of a voltage on the recombination of electrons and holes in the light-emitting layer (103) can be reduced, the level of the recombination of carriers such as electrons and holes in the light-emitting layer (103) can be increased, and the ratio of electrons and holes that are combined can be increased.