The effect of doping iodine on organic light-emitting diode

The performances of organic light-emitting diodes (OLEDs) with the configuration Al/Alq3 (Aluminum Tris-(8-hydroxygninoline))/TPD(N,N′-diphenyl-N,N′bis-(3-methylphenyl)-1,l′-bipheny-4,4′-diamine)/ITO have been significantly improved by doping iodine (I2) on both Alq3 and TPD layers. The luminance is promoted from 2800 cd/m2 without doping to 8000 cd/m2 with I2 doping under bias 10 V. Additionally, the driving voltage (@100 cd/m2) was reduced from 7.5 V without doping to 5.2 V with I2 doping. We attribute the promotions to the reduction of the electron and hole injection energy barrier at Al/Alq3 and TPD/ITO interfaces and the expansion of trap energy states beneath the LUMO of Alq3 generated by I2 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.