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Martin Held1 2 Daniel Ehjeij3 Johannes Zimmermann1 2 Stefan Schlisske1 2 Tobias Rödlmeier1 2 Gerardo Hernandez-Sosa1 2

1, Light Technology Institute, Karlsruhe Institute of Technology, Karlsruhe, , Germany
2, Innovation Lab, Heidelberg, , Germany
3, Heidelberg University, Heidelberg, , Germany

Electrodes in light-emitting electrochemical cells (LEC) do not only supply the necessary drive current, but need to provide sufficient transparency for the emission. Designing the entire device to be fully printed, biodegradable and compatible with the human body presents an additional challenge. While PEDOT:PSS electrodes are transparent and considered biocompatible, their relatively high sheet resistance produces high turn-on voltages in fully biodegradable printed LECs. To overcome this limit, inkjet printed gold grids are imprinted into the substrate below the PEDOT:PSS electrodes in various symmetric, deterministic and nature-inspired patterns. Inkjet printing supports full freedom of pattern design and scalability to industrial processes. Their contribution to the conductivity and reduction in transmittance is estimated with a simple model and experimentally confirmed. Different stretchable substrates with increasing ultimate strain from thermoplastic cellulose acetate to parylene to biodegradable elastomers are utilized to test the benefits and limits of these printed grid patterns. Owing to the choice of gold ink, the resulting LECs are completely biodegradable/ biocompatible and emphasize the potential of biomaterial based light-emitting devices. The use of flexible biomaterials in electronics in combination with scalable manufacturing of electrodes will enable the fabrication of transient and disposable technologies ranging from smart packaging and advertisement to degradable healthcare applications.

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