Material development
for smart textiles of tomorrow

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Organic materials

PEDOT:PSS

 

The polymer mixture poly(3,4-ethylenedioxythiophene):poly-(styrene sulfonate) (PEDOT:PSS) is highly electrically conductive and is therefore popular in electronic devices, for example as an electrode or in light-emitting devices as an auxiliary layer. PEDOT:PSS can be dispersed in aqueous environments, allowing solvent-based fabrication methods to be used.

DOI: 10.3390/s20195691

An ionic transition metal complex is a mostly cationic
organic complex with a transition metal, e.g. iridium, as center. PF6-, for example, is used as the counterion. Due to its luminescent property, iTMC is used in luminescent devices, so-called light-emitting electrochemical cells (LEC). In addition to the luminescent function, the complex also helps in charge carrier injection and transport, and thus single-layer devices can be realized using simple fabrication technologies such as spin coating. Due to the unique properties of the active layer and the way the device functions, layer thickness variations in the active layer are tolerable, allowing LECs to be processed on a wide variety of substrates such as fiber composites.
However, color matching of the LEC poses a major problem, as the emission color of the iTMC can only be changed by chemical modification, which destabilizes the light-emitting molecules and ultimately results in losses of device performance. Therefore, there are several approaches to change the emission color of the LEC. An example can be found here:
DOI: 10.1021/acsami.9b07019
Another idea is to combine quantum dots with the LEC. More on this can be found in the text below.

Ionic transition metal complex

Ionic liquid

 

Ionic liquid refers to liquid salts. They consist of cations and anions that are held together by electrostatic interaction. Some degree of motion remains, which does not result in a solid, crystalline structure. Ionic liquid is often added to the active layer of iTMC LECs to enhance device performance.

 

 

As mentioned above, changing the color of LECs is difficult. One approach is to integrate light-emitting quantum dots into the LEC environment. With quantum dots, the emission color can be adjusted by particle size, among other factors, making them very attractive in lighting technology.

Combination organic with inorganic materials

One idea is to incorporate the QDs into the device as a second emission layer. This was first realized with red QDs. In a further step, a white hybrid device could be realized by integrating blue QDs into the LEC architecture.

DOI: 10.1021/acsami.6b06833
DOI: 10.1021/acsami.8b15100
LED Professional Science Award, 2017

Likewise, for the first time, Cd-free QDs could be integrated into a LEC environment and operated as the only lighting component. This completely eliminates the need for the iTMC. Nevertheless, the layer thickness tolerance capability of the LEC can be maintained (free substrate selection) and at the same time the emission color can be adapted relatively easily to the requirements.

DOI: 10.1002/admt.201700154

An overview of all QD-integrated LECs can be found here:
DOI: 10.1002/adfm.201907349

Nanostructured materials

 

Nanostructured materials have interesting properties, especially optical and electronic, which is why they are already being used in many research fields. For example, ZnO nanoparticles can be used as a sensor layer and TiO2 nanoparticles can be incorporated into solar cells. Colloidal semiconducting quantum dots (QDs) are used in QD LEDs as a luminescent medium because their emission color can be adjusted by the size of the particles.
The diverse use of QDs can be seen, for example, in the following article, where QDs of different colors are excited to glow and ZnO QDs are used as an auxiliary layer:
DOI: 10.1021/acsami.6b15660
Another nanostructured material is graphene. Graphene is a two-dimensional structure made of carbon atoms and can find application, for example, as a flexible electrode in a wide variety of electronic devices, including smart textiles.