Properties of polymer light-emitting diodes coated on surface-treated ITO/glass substrates

We fabricated blue polymer light-emitting diodes (PLEDs) with indium tin oxide (ITO)/PEDOT : PSS/PVK/PFO-poss/LiF/Al structures. All of the organic film layers were prepared by the spin-coating method on plasma and heat-treated ITO/glass substrates. The dependences of the optical and electrical properties of the PLEDs on the plasma and heat treatment of the ITO film and the introduction of poly(N-vinylcarbazole) (PVK) layer were investigated. The AFM measurements indicated that the surface roughness of the ITO transparent film was improved by the plasma and heat treatment. In the emission spectra, the intensity of the excimer peaks of the PFO-poss [polyhedral oligomeric silsesquioxane-terminated poly(9,9-dioctylfluorene)] emission layer were decreased for the PLED device with the PVK film layer compared with the one without the PVK layer. The maximum current density, luminance and current efficiency of the PLEDs were found to be about 470 mA/cm², 486 cd/m² at an input voltage of 12 V and 0.55 cd/A at 100 cd/m² in luminance, respectively. The color coordinates (CIE chart) of the blue PLEDs were in the range of x = 0.17 ~ 0.20, y = 0.13 ~ 0.16, and the peak emission spectrum was about 430 nm, showing a good blue color.