Investigation of charge carrier mobility in 5,6,11,12-tetraphenylnapthacene (rubrene) and coumarin 6 doped Alq(3) films

Journal article, 2007

The doping effect on charge carrier mobility in tris (8-hydroxyquinolinato) aluminum (Alq(3)) was studied by time-of-flight (TOF) measurements. The polar dopant, coumarin 6 (C-6) and extensive pi conjugated dopant, 5,6,11,12-tetraphenylnaphthacene (rubrene) were used for this study. The co-doped of rubrene (Rb) with C-6 into Alq3 improved the carrier mobility compared to the single doped Alq3:C-6 film. The carrier mobility in single doped Alq3:C-6 film did not follow the linear relationship of Poole-Frenkel (PF) model with applied electric field. The mobility was in agreement with the PF model at two different ranges of electric fields (F) separated by a critical field root Fc approximate to 373 (V/cm)(1/2). The mobility in co-doped Alq(3):(Rb:C-6) film followed the linear relationship with the PF model. The energetic disorder was found as similar to 0.32 eV in co-doped films. It was similar to 0.55 and similar to 0.27 eV before and after the critical field in Alq3:C-6 film. The values of positional disorders in co-doped films were estimated as similar to 1.8 and it was similar to 2 in Alq(3):C-6 film at root F <= 373 (V/cm)(1/2). The organic light emitting diode performance of the co-doped film was improved compared to single doped film. The luminescence efficiency was improved tremendously to similar to 6 Cd/A in co-doped device at 45 mA/cm(2) current compared to Alq(3):C-6 film device of similar to 1 Cd/A. (c) 2007 Elsevier Ltd. All rights reserved.