Gravure Printed Ultrathin Layers of Small-Molecule Semiconductors on Glass

The authors present the feasibility of sheet fed direct gravure printing for ultra thin, organic semiconductor films on ITO coated glass. Printing with chrome plated gravure cylinders is often believed to require flexible substrates to promote fluid transfer to the substrate. However, the results demonstrate a stable process for the small-molecule Spiro-MeO TAD dissolved in toluene on rigid substrates. The authors obtained layer thicknesses in the range of 5-100 nm. They identified certain boundaries for gravure cell size yielding printed films with thickness of 10-15 nm with good homogeneity suitable for organic light emitting diodes or organic photovoltaics. For gravure cells smaller or larger than the optimal range, the printed layer is afflicted with dot-or ribbinglike structures. The authors show that the latter may result from nip-induced Saffman Taylor instabilities rather than spinodal dewetting or Marangoni effects. Finally, electrical characterization of a completed stack (PEDOT:PSS electrode) give evidence for integrity of the printed semiconductor layers. 2011 Society for Imaging Science and Technology. [DOI: 10.2352/J.ImagingSci.Technol.2011.55.4.040201]