Improvement of organic liglit-emitting devices by controlling deposition temperature and inclusion of carbon nanotubes

Research was conducted to improve performance of organic light-emitting devices (OLEDs) on flexible polyethylene terephthalate (PET) substrates based on tris-(8-hydroxyquinoline)-aluminum (Alq3). Based on double layer structure, indium tin oxide(ITO)/N,N'Diphenyl-N-N'-di(m-tdyl) benzidine (TPD)/Alq3/Al, flexible OLEDs on polyethylene terephthalate (PET) substrates were fabricated by physical vapor deposition (PVD) method, with the Alq3layer deposited at 90°C, 120°C and 150°C, respectively. It was found that the temperature had great effect on the surface morphology of Alq3and the devices fabricated at high temperature (150°C) showed a higher external efficiency than those fabricated at low temperature (90°C, 120°C). Multi wall carbon nanotubes (MWCNTs) doping poly(3,4-ethylene dioxythiophene) (PEDOT) : poly(styrene sulfonate) (PSS) was used as hole injection layer to improve performance of OLEDs based on Alq3. PEDOT:PSS, which was doped by 0.2 wt.%, 0.4 wt.%, 0.6 wt.%, 0.8 wt.% and 1 wt.% MWCNTs, was coated on clean PET substrate with ITO by spincoating method. The light-emitting layer (Alq3) and cathode layer (Al) were deposited by PVD method. It was found that the electroluminescence (EL) intensity of the OLEDs were highly improved by adopting MWCNTs doping PEDOT:PSS as hole injection layer. The luminous intensity obtained from the device with a concentration of 0.4 wt.% MWCNTs in the PEDOT:PSS layer was three folds as those adopted from device without MWCNTS doping in the PEDOT:PSS layer.