High conductivity Sepia melanin ink films for environmentally benign printed electronics

Significance Exclusive electronic transport over micrometric distances is uncommon in bio-sourced materials, usually featuring protonic or proton-assisted electronic transport. We found that films of Sepia melanin (the natural black–brown bio-pigment extracted from cuttlefish), flexographically printed from ink formulations including a binder, feature electronic conductivity as high as 10−3 S cm−1, an outstanding value for natural materials. Sepia melanin features a hierarchical structure, including granules as one of the sub-unit levels. We hypothesize that the binder confines Sepia melanin granules, leading to the formation of continuous inter-granular paths for efficient charge carrier percolation. Implicitly, our results reveal the high intra-granular conductivity of Sepia melanin. By shedding light on the transport physics of natural materials, we pave the way toward sustainable organic electronic technologies.