X-ray diffraction and scanning electron microscopic studies on the crystal structure and surface/interface morphology of zinc-octaethylporphyrin films on an indium tin oxide substrate spin coated with 3,4-polyethylenedioxythiophene:polystyrenesulfonate

The crystal structure and surface/interface morphology of zinc-octaethylporphyrin [Zn(OEP)] films deposited on an indium tin oxide (ITO) substrate spin coated with 3,4- polyethylenedioxythiophene:polystyrenesulfonate (PEDOT:PSS) have been investigated using x-ray diffraction (XRD) and scanning electron microscope (SEM), respectively. XRD results indicated that there are two kinds of grains with their sizes of approximately 20 nm that is independent of film thickness and substrate temperature. One has a diffraction plane with an interplanar distance of 1.12 nm and with its orientation parallel to the substrate, whereas the other has a diffraction plane with an interplanar distance of 1.24 nm and with that inclined mainly by 60° to the substrate. The abundant ratio of the two grains was controlled to some extent by varying film thickness and substrate temperature. Cross-sectional SEM images showed that a part of Zn(OEP) molecules are incorporated into PEDOT:PSS for its film thickness smaller than 130 nm, while that Zn(OEP) whiskers begin to grow for its film thickness exceeding 130 nm.