The effect of doping iodine on organic light-emitting diode

The performances of organic light-emitting diodes (OLEDs) with the configuration Al/Alq(3) (Aluminum Tris-(8-hydroxygninoline))/TPD(N,N'-diphenyl-N,N'bis-(3-methylphenyl)-1,1'-bipheny-4,4'-diamine)/ITO have been significantly improved by doping iodine (I-2) on both Alq(3) and TPD layers. The luminance is promoted from 2800 cd/m(2) without doping to 8000 cd/m(2) with I-2 doping under bias 10 V. Additionally, the driving voltage (@100 cd/m(2)) was reduced from 7.5 V without doping to 5.2 V with 12 doping. We attribute the promotions to the reduction of the electron and hole injection energy barrier at Al/Alq(3) and TPD/ITO interfaces and the expansion of trap energy states beneath the LUMO of Alq(3) generated by I-2 doping. The mechanism is illustrated comprehensively with a schematic energy diagram model and nicely supported with photoluminescence (PL), electroluminescence (EL) spectra and other experimental results. (c) 2005 Elsevier B.V. All rights reserved.