Understanding the formation of PEDOT:PSS films by ink-jet printing for organic solar cell applications

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Abstract
One of the most exciting aspects of organic electronic devices, in particular organic solar cells, is their potential for low cost and large scale manufacturing using printing technologies such as inkjet printing. In this manuscript, we report our work on developing an understanding of the ink-jet printing process to print smooth and transparent PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)) films for organic solar cell devices. The parameters that were found to strongly affect the formation of a continuous PEDOT:PSS film were substrate surface treatment, drop spacing, substrate temperature during printing as well as annealing. We investigated the effect of these parameters through detailed morphological characterization using optical and atomic force microscopy and the results suggested that one can achieve a transmittance of ∼90% for a ca. 110 nm thick film with a uniform structure and morphology, fabricated using a drop spacing of 30 μm and an annealing temperature of 120 °C. Overall, PEDOT:PSS film characteristics are strongly influenced by the substrate temperature during printing and annealing temperature as well as surface modification, determined by a mix of surface wetting characteristics, rate of evaporation of the solvent and coalescence of the printed lines. The organic solar devices fabricated using these inkjet printed PEDOT:PSS films show comparable performance yielding a power conversion efficiency of ca. 2.64% in comparison to ca. 3.1%, showed by the devices fabricated on standard spin coated PEDOT:PSS films.

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