Electrical and Morphological Properties of Inkjet Printed Pedot/PSS Films

Organic solar cells and LEDs are becoming more popular because their low cost materials, potential manufacturability, and recent gains in efficiency make them feasible for widespread commercialization in the near future. One significant manufacturing problem, especially for OLEDs, is the cost associated with creating patterned devices with spatially non-specific deposition methods such as spincoating. Inkjet printing can remove this problem. In recent years, inkjet printed polyethylene(3,4-dioxythiophene)/ polystyrene sulfonate (PEDOT/PSS) has been incorporated into many organic devices to help charge transfer, but there has not been much research regarding the effect of different printing parameters on the electrical and morphological film properties. In this work, an atomic force microscope, four point probe, and Kelvin probe were used to study the effects of printing parameters on roughness, conductivity and workfunction. Inkjet printed PEDOT films were also compared to spincoated films to determine how the polymer deposition method affects the above properties. Generally, inkjet printing created rougher but more conductive films with a smaller workfunction. Additionally, it was demonstrated that the workfunction of PEDOT films could be tuned over a range of about 0.5 V by changing the solvent mixture or substrate surface pretreatment. All additives to the as received PEDOT/PSS suspension causedmore » the workfunction to decrease. It was discovered that workfunction decreases as printing voltage increases, but the trend reverses after annealing the films. This phenomenon suggests that when DMSO interacts with PEDOT, the workfunction changes. Finally, the results support previous publications suggesting that DMSO increases conductivity through a screening effect and also by changing the distribution of PEDOT and PSS in the film.« less