Effect of Substrates on Structural, Morphological, Optical and Electrical Characteristics on Poly (9,9-di-n-octylfluorenyl-2,7-diyl) (PFO) Thin Films

Polymer light-emitting diodes using organic-inorganic heterojunctions have a lot of benefits such as excellent blue-light emission, simple fabrication procedure, and low processing cost. We report on the effect of substrates on the fabrication of poly (9,9-di-n-octylfluorenyl-2,7-diyl) or (PFO) thin films and their characterization as a simple light-emitting diode (LED) structure. The structural properties of the thin films were characterized using X-ray Diffraction (XRD). The morphological properties of the thin films were studied using Field Emission Scanning Electron Microscope (FESEM) and Atomic Force Microscopy (AFM). The XRD results demonstrated the formation of amorphous PFO structure, with no presence of the crystalline phase of PFO. The FESEM images showed the formation of cracks due to evaporation from annealing. Optical characteristics were studied using ultraviolet-visible (UV-Vis) spectroscopy, Photoluminescence (PL) and reflectance measurements showing the presence of β phase of PFO, important for charge carrier mobility. Thin films deposited on ITO-coated glass, FTO-coated glass and Silicon n-type (110) and (111) orientation substrates were used to fabricate a simple LED structure. The devices fabricated using Si n-type substrates showed p-n junction characteristics and was a better substrate choice than ITO or FTO coated glass.