Optical, photophysical, and electrooptical studies on slot-die polyfluorene-based flexible OLED devices

Polymer F8:F8BT blend systems were created by mixing Poly(9,9-di-n-octylfluorenyl-2,7-diyl) (F8) and poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) with 19:1, 1:1 and 1:19 ratios, then grown by R2R slot-die coating technique, for use as emitting layers (EML) in organic light emitting diodes (OLEDs). The multi-layer structure of the OLEDs consisted of a flexible poly(ethylene terephthalate) (PET) substrate, an indium tin oxide (ITO) film as the anode, a poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) film as the hole transport layer, also grown by slot-die, the EML and the evaporated Ca/Ag bilayer as the electron transport layer and cathode. The synergy of spectroscopic ellipsometry, photoluminescence, and electroluminescence characterization techniques provided the overall investigation and evaluation of the optical, photophysical, electrooptical, and operational properties of films and devices. The dielectric function and the absorption coefficient of the blends were dominated by electronic transitions that were assigned to respective electronic transitions in F8 and F8BT identified by the study of single component F8 and F8BT layers grown by the spin coating technique as control films and devices. This work aims to give insight into the interrelation between the optical and electronic properties with the nanostructural, photo- and electro-luminescence characteristics of the slot-die F8:F8BT OLED devices. Based on these, the justification of the main operational characteristics and the performance of the OLEDs is achieved.