Just add dendrimers, cellulose, and graphene: new environmentally friendly, long-lasting luminescent electrochemical cells

In research that could usher in a new era of lighting, researchers in Japan and Germany have developed an environmentally friendly light-emitting electrochemical cell that uses new molecules called dendrimers with biomass-derived electrolytes and graphene-based electrodes. Combine.Their findings were published in the journal Advanced Functional Materials.

Electroluminescence is the phenomenon in which a material emits light in response to passing an electric current. Everything from the screen you use to read this sentence to the lasers used in cutting-edge scientific research is the result of electroluminescence in different materials. Due to its ubiquity and necessity in modern times, it is only natural that substantial resources are invested in research and development to make this technology better.

“An example of an emerging technology is the ‘Light Emitting Electrochemical Cell’ or LEC,” explains Ken Albrecht, an associate professor at Kyushu University’s Institute of Materials Chemistry and Engineering and one of the leaders of the study. “They have been attracting attention due to their cost advantage over organic light-emitting diodes (OLEDs). Another reason for the popularity of LECs is their simplified structure.”

OLED devices typically require careful layering of multiple layers of organic thin films, making fabrication tricky and expensive. On the other hand, LECs can be made from single-layer organic thin films mixed with light-emitting materials and electrolytes. The electrodes that connect them together could even be made of inexpensive materials, unlike the rare or heavy metals used in OLEDs. In addition, LECs are driven at lower voltages, which means they consume less energy.

“Our research team has been exploring new organic materials that can be used in LECs. One of the candidate materials is dendrimers,” explains Prof. Rubén D. Costa at the Technical University of Munich, who led the research team in Germany. “These are branched, symmetrical polymer molecules whose unique structure has applications in everything from medicine to sensors and now optics.”

Building on past developments of dendrimers, the research team set out to modify their LEC material.

“The dendrimer we originally developed had hydrophobic or water-repellent molecular groups. By replacing it with hydrophilic or hydrophilic groups, we found that the lifetime of the LEC device could be extended to more than 1,000 hours, which is not the case with conventional polymers.” more than 10 times the original. Albrecht explains. “Even better, the device is very environmentally friendly thanks to our collaboration with Dr. Costa’s team.”

For years, Costa’s team in Germany has been working on developing cheaper and greener materials for light-emitting devices. One material they’ve been experimenting with is cellulose acetate, a common organic compound used in everything from clothing fibers to eyeglass frames.

“We used biomass-derived cellulose acetate as the electrolyte in our new LEC device and demonstrated that it has the same long lifetime,” Costa continued. “Also, we found that graphene can also be used as an electrode. This is an important step towards making flexible light-emitting devices using environmentally friendly materials.”

The team explained that while their work is promising, more research is needed before bringing the device to market.

“The device we made here can only emit yellow light, so we needed to develop it to emit light in three primary colors: blue, green and red. The luminous efficiency, i.e. the brightness of the light, also needs to be improved,” concludes Albrecht road. “Although thanks to our international cooperation, the future looks bright.”