This is to combat the two million tons of electronic scrap being produced annually in Germany from products with printed electronics such as interactive packaging or smart plasters.
The researchers are using easily biodegradable materials such as plant extracts or gelatin to make semiconductors, dyes or insulators. “These may not be as long-lived as the inorganic alternatives, but they easily survive the service life of disposable electronics,” said Dr Gerardo Hernandez-Sosa, leader of the Biolicht Young Investigator Group of KIT. After use the electronics can simply be thrown away into the biowaste bin or on compost heaps, where it will rot like a banana skin.
So far, this has not been the case for conventional printed electronics, such as OLEDs. “We call all synthetic materials that are based on carbon ‘organic’. But this term does not tell us anything about environmental compatibility,” Dr Hernandez-Sosa explained. The carrier foil of OLED is made of the same plastic material as conventional drinks bottles.
One of the challenges the researchers face is how to produce compostable inks that will form the circuits. Environmentally compatible materials with the desired electrical properties have to be identified. For instance, hard gelatin - used for making drug capsules - is suited for insulation.
Contrary to conventional ink, it must not penetrate into the carrier material, but should form a closed liquid film on it without dripping off. A solvent that is too thick would plug the pores of the printer. A solvent too thin disperses on the carrier foil and does not cover it homogeneously. The properties of the dry material film are crucial to the function of the electronic components: Its thickness of less than a thousandth of a millimetre must not vary by more than 5%.
The researchers expect to have compostable organic electronics ready for the market within three years.
