Surface wetting properties of treated indium tin oxide anodes for polymer light-emitting diodes

We report contact angle hysteresis and surface energy of differently treated ITO substrates obtained by measuring dynamic contact angles for liquids with different polar character. We find that the hysteresis and the polar and dispersion component of the surface energy depend strongly on the surface treatments. Oxygen-plasma induces the highest surface polarity and the highest total surface energy, but in contrast, argon-plasma shows the lowest surface polarity and the lowest total surface energy. We suggest that such surface wetting properties of the ITO anodes play an important role in deciding the interface formation with polymers, and therefore the performance of light-emitting diodes. We discuss the results in relation to the ITO surface roughness and chemical heterogeneity modified by the different treatments.