Optical and electrical behavior of synthetic melanin thin films spray-coated

We investigated the optical and the electrical conductivity properties of synthetic melanin thin films spray-coated on glass. These films showed a broadband monotonic increase of the absorption coefficient, decreasing the wavelength in the Visible-NIR range. Conductivity as a function of the temperature evidenced a semiconductor like character and a hysteretic behaviour after thermal annealing up to 475 K. Thermal activation energies extrapolated by resistance curves have been explained by using the framework of a band-model as for an amorphous semiconductor.