Laser-Induced Carbonization of Natural Organic Precursors for Flexible Electronics

A precursor ink for carbon laser-patterning is developed using inexpensive, naturally abundant molecular compounds, namely citric acid and urea, and used to fine-print conductive carbon circuits on a flexible substrate. The precursor in the ink consists of organic nanoparticles obtained from the thermal treatment of citric acid and urea. This precursor is thoroughly characterized chemically and structurally. A simple recipe for the ink is then described for the creation of highly reproducible laser-patterned carbon structures on different substrates. Homogeneous ∼20 µm thick films are cast on different substrates and characterized before and after laser-carbonization. The carbon content of the final films is 97% and is of turbostratic graphitic nature. As reproducible laser-induced reactions depend on precise laser conditions, the influence of material properties, film thickness, and laser fluence are thoroughly analyzed. Films on three different substrates, namely aluminum sheets, silicon wafers, and polyethylene terephthalate (PET) are characterized by electrical impedance measurements. Electrical conductivities of up to 5.21 S cm⁻¹ and maximum current densities of 44 A cm⁻² are achieved, which proved applicable as fine carbon circuits on PET as a flexible substrate. This study opens a simple synthetic avenue to producing conductive circuit elements based on carbon.