Degradable electronic skin! The NTU team develops flexible optoelectronic substrates with a transmittance of 91.1% made by fish scales

As the impact of plastic particles and nanoparticles on the environment is becoming more and more obvious, the influence of plastic films in optoelectronic devices, especially in the development of degradable wearable electronic products, has gradually attracted people's attention. A research team at Nanjing University of Technology in China provides a possible answer: using fish scale materials to make degradable film substrates.
 
"Electronic Skin"

The team at Nanjing University of Technology focused on a special type of optoelectronic products-flexible AC electroluminescent devices (ACEL, Alternating-current electro-luminance) with transparent plastic film.

The ACEL device consists of a thin flexible transparent substrate and the wiring and luminescent materials on it. The current products can already achieve uniform light emission and have a certain power processing efficiency. In addition, these products generate less heat. Because of these characteristics, this device is very attractive for the development of wearable electronic products. Developers have even envisioned many disposable applications of degradable "electronic skin", such as luminous temporary tattoos or disposable film stopwatches, athletes can make such stopwatches on the skin before the game, and then easily remove them at the end .
 
Sustainability crisis

Although this display technology is very convenient to use, it also makes many people worry. Because the main components of these wearable display devices are thin and soft plastic substrates, such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN) and polycarbonate (PC ). In terms of sustainability, the use of these materials brings troubles: on the one hand, they are made from non-renewable fossil fuel raw materials, and their production process has a significant impact on global climate change.

On the other hand, the waste plastic itself will further affect our living environment in the form of garbage. As pointed out in a recent review in the Journal of Geophysical Research, microplastics and nanoplastics play an important role in the formation of huge marine “garbage belts”.
 
Neglected raw materials

In view of this, researchers are looking for substrate materials that can be used as an alternative to electronic skin applications. These materials must have very little environmental impact. At present, candidates include cellulose and silk protein in trees. Among them, the acquisition of cellulose itself does not meet sustainability considerations, while silk protein is too costly to be used for large-scale production of disposable photovoltaic products.
 
A team led by Nanjing University of Technology Yu Haidong, Liu Juqing and Huang Wei focused on another material: gelatin in fish scales. Researchers believe that this material has some potential and excellent photoelectric properties. More importantly, the supply of raw materials is not a problem. According to the author of the paper, these inedible fish scales account for "3% of the annual fish production of 70.5 million tons." On the other hand, scale gelatin is biodegradable, that is to say, this material can be naturally integrated into the environment after being discarded.
 
From fish scale to light emitting device

To verify these ideas, the team at Nanjing University of Technology first cleaned and chemically pretreated the fish scales to make the precursor solution, and then the researchers put them in a Petri dish and made a fish scale gelatin film. Tests show that the transparent film has a transmittance of up to 91.1% in the visible light spectrum, which is better than the PET film currently used (transmittance 90.4%). This film also shows very good flexibility and can even be folded reversibly. The researchers found that this film is easy to recycle (it can be dissolved in 60 ° C water for a few seconds), and it can also be biodegraded (it can be completely decomposed in only 24 days in soil).
 
Next, the research team used this fish scale gelatin film as the substrate for several light-emitting devices. They first coated a layer of silver nanowires used as electrodes on this fish scale gelatin film, then further made an emitting layer containing luminescent materials by spin coating, and finally made another electrode using silver nanowires on the emitting layer Floor. The research team found that, under the application of alternating current, even after a thousand cycles of bending and relaxation, this light-emitting device can still emit bright light and "the luminous intensity has not decreased significantly."
 
Researchers at Nanjing University of Technology have concluded that their method "can produce more environmentally friendly optoelectronic products without producing harmful by-products and electronic waste during the manufacturing process." They believe that the film made of fish scales has great application prospects not only in the field of wearable technology but also in the field of flexible displays.