Characterization of drop-on-demand microdroplet printing

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has been used extensively in the fabrication of polymer light-emitting diode displays by drop-on-demand inkjet printing technique. In order to make a good thin film with high uniformity, it is crucial to control the drying behavior of inkjet-printed PEDOT:PSS droplets. In this work, the morphology of printed drops of ～10 pL after drying was examined and explained in a qualitative manner, which would extend the comparison with previous work described in published literature. Results show that drying behavior is sensitive to substrate temperature due to the high surface-to-volume ratio of a microfluid. There exists an appropriate range of temperatures to obtain a good drop with sharp edge and flat surface. On the other hand, when the temperature exceeds a limit, a ring-like structure was observed. Results from this experiment would be considered as a reference to achieve uniform film after drying and has potential to be applied in the modeling of drop impact.