High-conductivity poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) film for use in ITO-free polymer solar cells

In this study, we devised a simple method to enhance the conductivity of poly(3,4-ethylenedioxythiophene)-poly(styrene-sulfonate) (PEDOT:PSS) films through spin-coating with various surface-modified compounds, and then applied this technique to the preparation of ITO-free polymer solar cells (PSCs). The electrical conductivity of PEDOT: PSS films can be increased by more than two order of magnitudes merely by spin-coating a compound containing one or more polar groups - such as ethanol, methoxyethanol, 1,2-dimethoxyethane, and ethylene glycol - onto the films. In this paper, we discuss the phenomena occurring through conductivities, morphologies, and chemical properties of the modified PEDOT-PSS films as determined using Raman spectroscopy, a four-point probe, scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The schematic 3D morphological model of directly solvent-modified PEDOT: PSS films is presumed for ITO-free devices. The desirable conductivity enhancements of these materials make them attractive candidates for use as anode materials in ITO-free PSCs.