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

Abstract

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.

High conductivity PEDOT:PSS through laser micro-annealing: mechanisms and application

“…Here it is seen that low power irradiation, below 2.5 W (equivalent to a power density of around 20 W mm À2 ), has little effect on the sheet resistance, consistent with previous reports. 37,38 Above 2.5 W the sheet resistance drops rapidly to a minimum of 369 AE 2 O & À1 at 4.2 W, followed by a gradual increase in sheet resistance as the laser power increases and the film is over irradiated. The correlation between the laser power and materials properties are discussed in the next section.…”

“…In this case, the entire film receives uniform irradiation, as described elsewhere. 37 200 μm is, therefore, the spacing used for the remainder of this work.…”

“…A promising alternative has recently been reported in which laser based micro-annealing gives spatial control of the conductivity of PEDOT:PSS without additional chemical dopants. 34,37,38 These reports conclude that the laser annealing fragments the PSS shell at the top surface, and enables local migration of the PEDOT cores, leaving aggregated PEDOT cores exposed at the surface, facilitating charge transport between these cores. 34,38 However, the relative importance of these two actions remains unclear.…”

Recent Progress on Poly(3,4‐Ethylenedioxythiophene):Poly(Styrenesulfonate) Bioelectrodes

“…Common methods include surface modifiers coating, laser microannealing, hot pressing, and mild plasma. [83][84][85][86][87][88][89] Due to its spatial selectivity, laser microannealing technology can achieve patterning and high conductivity of PEDOT:PSS simultaneously. By controlling the irradiation intensity below the damage threshold, phase separation would be induced between PEDOT and PSS.…”

“…The nanostructures of PEDOT cores would rearrange and crystallize. [86][87][88][89] Yun et al enhanced the conductivity of PEDOT:PSS by three orders of magnitude through laser illumination. The mechanism lies in the difference in photon absorption between PEDOT and PSS.…”