Cadmium-Free Quantum Dot-Polymer Composite for Display

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Solution Overview

Problem

Existing quantum dot-polymer composites face challenges in maintaining excellent photoluminescence properties during patterning processes, leading to deteriorated light emitting efficiency and stability, especially when cadmium-free semiconductor nanocrystals are used, which are essential for environmental and health safety.

Innovation Solution

A cadmium-free quantum dot-polymer composite is developed with a core-shell structure, where the shell has at least two branches and a valley portion connecting them, and a thickness of greater than or equal to 1.7 nanometers, using a polymer matrix with a carboxylic acid group-containing binder to enhance compatibility and stability, allowing for improved luminous efficiency and thermal stability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If cadmium-free semiconductor nanocrystals are used, then environmental and health safety is improved, but photoluminescence efficiency and stability deteriorate

Engineering Contradiction:

Improveenvironmental and health safetyVSAvoidphotoluminescence efficiency and stability

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The patent uses a core-shell structure where the core is made of cadmium-free semiconductor nanocrystal (InP) and the shell is made of ZnSeS alloy material. This composite structure allows the cadmium-free core to maintain environmental safety while the ZnSeS shell passivates the core surface, reducing non-radiative recombination and improving photoluminescence efficiency and stability to exceed 75% quantum efficiency.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent optimizes the shell thickness to be greater than or equal to 1.7 nanometers and controls the composition ratio of ZnSeS alloy in the shell. By adjusting these parameters, the shell provides sufficient passivation effect to maintain high photoluminescence efficiency while keeping the overall structure cadmium-free.

Inventive Principle:

Principle #35Parameter changes

2Ease of manufacture

If quantum dot-polymer composite is subjected to patterning process, then device fabrication is enabled, but photoluminescence properties deteriorate

Engineering Contradiction:

Improvepatterning capabilityVSAvoidphotoluminescence properties

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent performs preliminary passivation by forming the ZnSeS shell on the InP core before the patterning process. This pre-established protective shell structure prevents damage to the quantum dot's photoluminescence properties during subsequent patterning operations, maintaining quantum efficiency above 75% even after patterning.

Inventive Principle:

Principle #10Preliminary action

3Reliability

If shell thickness is increased, then photoluminescence efficiency is improved, but quantum dot size increases

Engineering Contradiction:

Improvephotoluminescence efficiencyVSAvoidquantum dot size

Core Design Contradiction:

ReliabilityVSLength of moving object

Solution Approach 1:

The patent optimizes the shell thickness parameter to be greater than or equal to 1.7 nanometers, which provides sufficient passivation for high photoluminescence efficiency while controlling the overall quantum dot size to remain in the 2-10 nanometer range, maintaining quantum confinement effects and narrow emission bandwidth.

Inventive Principle:

Principle #35Parameter changes

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 composite maintains high photoluminescence efficiency and stability, achieving a quantum efficiency of greater than 75% and a photo-conversion rate of greater than 45%, even after patterning, while replacing absorption-type color filters in liquid crystal displays with photoluminescent filters for improved luminance and color reproducibility.

Implementation Method 1

These quantum dots may emit light of various photoluminescence wavelengths. As the quantum dot has a theoretical quantum yield (QY) of 100% and emits light having a high color purity

Methodology Applied

Scientific EffectPhotoluminescence: Photoluminescence

Implementation Method 2

the quantum dot as a light emitting material may realize increased luminous efficiency

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS11661547B2Quantum dot polymer composites and devices including the same

Publication Date: 2023.05.30 SAMSUNG ELECTRONICS CO LTD

AI summary

A quantum dot, including a core including a first semiconductor material that includes indium; and a shell including a second semiconductor material, and disposed on the core, wherein the first semiconductor material and the second semiconductor material are different, wherein the shell has at least two branch portions and a valley portion connecting the at least two branch portions, at least one of the at least two branch portions comprises Zn, Se, and S, and a content of sulfur in the at least one branch portion increases in a direction away from the core.