Sputter-cleaning modified interfacial energetic and molecular structure of DNTT thin film on ITO substrate

The effect of natural electrode contamination on interfacial energetic, structure and morphology of ??????conjugated organic molecular layers were studied by depositing dinapthothienothiophene (DNTT) thin films of varying thickness on indium-tin-oxide (ITO) substrates and by using photoelectron spectroscopy, atomic force microscopy and X-ray reflectivity techniques. The DNTT thin film on unclean-ITO surface shows a smaller threshold ionization potential (by similar to 0.4 eV) compared to the film on clean-ITO one. A molecule-substrate interaction, present in the DNTT/clean-ITO system, gives rise to an interfacial dipole and charge transfer, presumably through flat-lying seed-layer at the interface. On further deposition, the interfacial coverage increases, while the molecules on top of the seed-layer take different orientation (mostly edge-on) to form highly-dewetted fibrous-islands of very high-thickness but very low-coverage. Overall, the growth of DNTT film on clean-ITO surface is layer-plus-island-like or Stranski-Krastanov-type. On the other hand, the contamination layer at the DNTT/unclean-ITO interface is found to act as a spacer layer, which reduces the intimate molecule- substrate interaction and also the roughness to give rise an edge-on ordered island-like or Volmer-Weber-type film-growth with reduced hole injection barrier (by similar to 0.2 eV) and better (almost double) film-coverage to make it a more efficient hole injector compared to the clean interface one.