Spatial Conductivity Distribution in Thin PEDOT:PSS Films after Laser Microannealing

In contrast to conventional methods for increasing the conductivity of transparent polymer electrodes based on additives, solvent treatment, or hot plate thermal processing, laser heating enables the selective annealing of defined areas of a material on the micrometer scale. This study investigates the spatial conductivity distribution of thin PEDOT:PSS films after selective heating by continuous wave (cw) laser radiation without damaging the material. The sheet resistances of the samples decreased abruptly above a certain threshold intensity and a changed relative permittivity of the irradiated material was detected by imaging ellipsometry. A theoretical model has been derived to estimate the resulting spatial conductivity distribution induced by the inhomogeneous heating with the Gaussian spatial intensity distribution of the applied laser radiation. In combination with the experimental measurements, the model revealed that the conductivity increased proportionally to the intensity above the threshold intensity, but remained unchanged below, resulting also in a Gaussian spatial conductivity distribution. Thus, in contrast to conventional oven annealing where only large-area averaged annealing is possible, laser annealing allows to tailor the spatial distribution of the conductivity on a micrometer scale opening applications for future micro systems.